 Namaste and welcome to the video course on watershed management. In today's lecture, in module number 3, lecture number 11, we will discuss the rainwater harvesting systems and roof catchments. So, some of the topics covered today will be rainwater harvesting system, roof water catchment system, urban water scarcity, rainwater harvesting system, cost, safety and water quality and maintenance and two case studies. Some of the important keywords for today's lecture include rainwater harvesting system, roof water catchments and urban water scarcity. So, the last lecture we were discussing about the rainwater harvesting systems. So, we have seen that the rainwater harvesting systems can be of three type. One is the rooftop based, second one is the open space like what is there in say open areas, gardens and other place and then third type can be the watershed based. So, depending upon the area where we have to go for the rainwater harvesting system, we can have one of these or an integrated approach by considering either rooftop and the open space or the combining all this within the perspective of a watershed management within the watershed. So, we have seen the details about the various hydrogeological aspects and then also the artificial recharge aspects as far as the especially rainwater harvesting in open areas and the watershed related issues we have seen in the last lecture. So, one of the important aspect of rainwater harvesting especially in cities, in water scarce areas like Erid and Semarid regions, islands and coastal region is rooftop based the rainwater harvesting. So, the various design related issues we have already discussed as far as the rainwater harvesting is concerned. So, today we will concentrate on the rooftop rainwater harvesting. So, rooftop rainwater harvesting as we discussed in the last lecture, it is a technique through which rainwater is captured from roof catchments and stored in reservoirs. So, here in the rainwater harvesting system, we are harvesting the rainwater either from the roof or the open space or on a watershed scale. So, as far as rooftop catchment is concerned, so we consider rooftop as the catchment and we capture this water and collect it and then either store it for the direct use. So, harvester rainwater can be stored in storage tanks to meet the household needs directly. So, especially in a dry region, Erid region or Semarid regions or coastal regions or islands so, where water problem is there or we can also recharge to the subsurface I mean as groundwater. So, it will be recharge to the groundwater system by adopting the artificial recharge techniques. So, it is other than the natural recharge, so we are providing specific structures, so that there will be more recharge so called the artificial recharge will take place. So, the main objective of rooftop based rainwater harvesting is to make water available for future use. So, as we discussed the rainfall is concerned, it may be available only for few months. Say in India say for example, 3 to 4 months most of the places and then the spatial variation. So, whatever whenever rainfall takes place, we are trying to capture it through harvesting and then so that we can use it for future use say in the dry season, so that sufficient water will be available. So, capturing and storing rainwater for the use is particularly important in dry land as I already mentioned, hilly regions where say immediately after rain for all the water drains out due to the high slope then urban and coastal regions. So, coastal regions especially say in groundwater say wherever the aquifer is affected by the seawater ingress there we can directly harvest this say rainwater and then directly use from the rooftop or we can recharge to reduce the seawater ingress. So, now in alluvial areas say for example, if we can recharge so other than directly utilize if we can recharge and then say if there is a rise of water table say by 1 meter then say the pumping cost can be reduced by 0.4 kilowatt per hour. So, that way it will be also energy saving will take place. So, if we can recharge and then in the aquifer system when the water table rises then definitely there is the saving of the energy so that what will be used for the pumping purpose. So, within the perspective of rainwater harvesting we have already seen the various aspects of rainwater harvesting. So, now within the perspective rooftop rainwater harvesting so why we need to go for rooftop based rainwater harvesting. So, some of the needs are listed here to meet the ever increasing demand for water. So, especially in city regions and say arid and semi arid regions and with the increase in population and industrial developments the water increase is going up. So, that way we can say other than the natural recharge either we are recharging further through artificial means or we are storing the rainwater directly. Then to reduce the runoff which chokes storm drains. So, you can see that especially in urban areas like cities like Mumbai and other coastal cities in most of the monsoon season there is flooding problem. So, if we can say reduce the runoff coming from the urban areas by means of say rainwater harvesting then we can see that the whatever the runoff coming through the drains will be reduced and that way we can reduce the flooding problem. So, that way to avoid flooding of roads and other areas so that will be an indirect advantage of this rainwater harvesting. Then to augment the groundwater storage and control decline of water levels. So, as we discussed so when we are doing the recharge other than the natural recharge through artificial means when we are increasing the recharge then the groundwater level goes up. So, that is another need then to reduce groundwater pollution. So, the rainwater is one of the purest form of water so without any kind of pollution. So, if we can recharge that water to the groundwater then the whatever the polluted groundwater will be the pollution will be decreased. Then to improve the quality of groundwater so that way we can improve the quality of groundwater. Then to reduce the soil erosion especially say in open areas or a watershed if we can provide the various structures for artificial recharge then we can see that soil erosion can be reduced and more over say when the say the water flowing through the say coming from the roof top is reduced through means of rainwater harvesting. Then also the flow will be runoff will be reduced so that will also give the advantage of reducing the soil erosion. Then to supplement domestic water requirement during summer drought etcetera. So, if you are directly storing the rainwater in tanks or say other structures then we can directly utilize that water for the drought period or summer season. And so that way say two aspect one is directly storing in tanks or other structures or we can recharge. So, that way the number of say advantages and these are some of the important needs as far as the roof top based rainwater harvesting is concerned. So, as I mentioned the roof top rainwater harvesting can be of two types. So, the methodology can be so directly we can store in tanks so you can see that whatever directly coming from the building we can collect through the gutters the pipelines and then directly say after filtration we can store it in a tank as shown in this photograph and then directly we can utilize. And second way is say the storage in groundwater reservoir so what we can do we can collect the rainwater and then say after some filtration we can pass into say various recharge structures like dug well bore well recharge fit fit sharp trenches etcetera and that can be put into this so that so it will be recharging to the aquifer system. So, that is another way as far as the roof top based rainwater harvesting is concerned and then say depending upon the area we can go for both I mean an integrated system say some part of the water can be collected in tanks and some water can be used for recharging to the aquifer system. So, an integrated approach is also possible as far as roof top rainwater harvesting is concerned. So, now say we have already discussed rainwater harvesting system and its design aspects in the last lecture. So, very similar way as far as roof top rainwater harvesting system is also concerned and say we have to see how much area is there from which water can be collected and then how is the rainfall pattern and then how much is the collection efficiency or depending upon there are no coefficient we can identify how much water can be collected for a given roof top area. So, the question how much water can be collected as far as roof top rainwater harvesting system is concerned. So, this depends upon the collection efficiency as I mentioned. So, how efficiently the rainfall can be collected depends on several considerations such as what kind of roof, what kind of roof material, what is inclination of the roof etcetera and then what are what are rainfall conditions, what is the intensity of rainfall, what is the duration of the rainfall like that and then weather conditions like what is the temperature, what is the humidity. So, depending all these conditions say the collection efficiency varies from place to place and also it depends on the season. And then normally say for a normal conditions we can see that about 80 percent collection efficiency we can achieve depending upon the specific design. So, if say for example, if 1000 mm rainfall is annually available we can store say we can think of harvesting about 800 millimeter of this rainfall for a given say the roof top catchment. And then as I mentioned the collection how much can be collected depends upon the rainfall availability. So, that means average rainfall pattern and what is the intensity, duration etcetera. So, then say as far as a catchment is concerned the roof top is concerned we can find out total quantity of water that can be collected in cubic meters is equal to roof top area say in square meter multiplied by average rainfall say annual rainfall into collection efficiency. So, this equation gives how much water can be collected as far as roof top based rainwater harvesting system is concerned. So, you can see that say if collection efficiency say for example, if it is 80 percent or 0.8 then the say how much the collection depends upon the roof top area and then rainfall availability say as far as that particular location is concerned. So, we can prepare say depending upon rainfall pattern and how much roof area so that is constant. So, that way we can identify when we design a roof top based rainwater harvesting system as this much water can be either collected in tanks or this much what will be available for the artificial recharge. So, that way we can have a table say for various roof top areas and for various rainfall annual rainfall conditions. So, if we assume a collection efficiency of 80 percent we can prepare a table like this and directly we can identify how much volume of water say in cubic meter can be harvested say as for the given roof top area so that way we can directly identify. So, now say before going further as far as the various design aspects of roof top rainwater harvesting system. So, let us have a brief look into the urban water problems so what are the solution strategies. So, many of the urban cities especially say for example, in developing countries like India say cities like Delhi, Chennai all the cities have water scarcity problem. So, say especially the areas where the directly the water is obtained from the groundwater system. So, this say rain the roof top is to rainwater harvesting system is a good technology as far as the to solve the water related problems. So, we can use say the solution strategies as far as solution strategy is concerned we can identify the potential zones in over exploited areas and design and implement suitable site specific roof water and surface water harvesting structures to raise the groundwater table. Say this is very much possible in places like Chennai, Delhi, Chandigarh etcetera where so much of groundwater is used for the domestic and industrial purposes. Then as another strategy we can promulgate roof and surface water harvesting techniques through community rainwater harvesting methods. So, it is say the initiative should be a community based initiative so all the people should come in say come together so that say village or city based say for particular city based or urban watershed based scheme we can develop so that we can that will be a solution as far as the urban water scarcity is concerned. Then sustain existing water supply scheme by artificial richer so as I mentioned say for example, due to the efforts of various governments and non-government organizations in places like Delhi and Chennai in the last few years say huge efforts were put as far as the rainwater harvesting is concerned so that we have shown good impacts as far as the water availability is concerned especially cities like Delhi and Chennai. So that way we can sustain existing water supply scheme by artificial recharge and then introduce water harvesting structures on unpolluted storm water drains open areas parks and playgrounds so that so other than the normal infiltration taking place recharge taking place to the aquifer system and we are increasing the recharge through various means so that way we can say increase the water availability and that will be a solution strategy as far as urban water scarcity is concerned. And then use stagnant water for recharge purposes in relatively low lying areas store flood water in appropriate locations and construct suitable recharge structures in water logging areas. So if you can store water for say with some pressure then you can see that more recharge will be taking place to the aquifer system so that that will increase the water table groundwater table and that can be another solution strategy as far as urban water scarcity is concerned. Then we can introduce site specific artificial recharge structures on wide roads which become waterways during heavy down power in the monsoon season. So actually this technique has been implemented by Delhi government in many parts of Delhi states especially on road sides so that has been found to be very successful. So since a lot of area is there and that area we can stop the water and then allow to recharge to the groundwater so that way the groundwater table level will be increased. So then some of the other solution strategies include convert dry tubules and bore wells into recharge wells. So you can see that due to over drafting of the water from the groundwater system many of the tubules and bore wells goes into dried condition. So that tubules and bore wells we can utilize for utilize as recharge well and then design projects for recycling and reuse of wastewater. So recycling and reuse and water conservation we will be discussing in detail in the later part of this course. So we can also say use the various techniques as far as recycling and reuse is concerned. Then construct site specific artificial recharge structures like percolation pits, dug come bore wells, mini artificial aquifer systems, trench come percolation pits, percolation ponds, recharge wells etc. So then another important aspect is that say rain is say obviously say as per say average annual rainfall condition most of the time most of the years it will be available and area is there of rooftop as a catchment is available. So only thing is that people have to actively do this rainwater harvesting schemes at various locations. So that many times people do not understand or do not know what are the advantages of such systems. So it is always better to go for a mass awareness programs either ground main level or non ground main say organizational levels or education institutions level. So that mass awareness comes more people will be interested in this kinds of roof proper rainwater harvesting or other types of rainwater harvesting systems. Then make roof water harvesting as a people movement. So actually say this is what is happened in Chennai and other regions in Tamil Nadu. So due to the various ground main rules and regulations plus say a lot of awareness program mass movement has been taken place in the last few years in Chennai and other regions in Tamil Nadu and then we can see that most of the houses or most of the land areas where rainwater harvesting is possible many locations it has been done. So that way if we can make the rooftop or rainwater harvesting as a people movement then it will be a huge success. Then comments and sustained training programs for executives of government and non-government organizations and strengthen ongoing awareness projects. So say many of the say agencies say say which are not so familiar or not experts in the area of rainwater harvesting say various agencies who are expert in this rainwater harvesting schemes can give training programs and then say give seminars lectures etc. So that this awareness can be improved say can be spread to the all the public and the government organizations. So that will lead to the rainwater harvesting schemes. So that way if you when it becomes a people movements definitely the efforts will be much much better. So now let us see what are the important design considerations as far as rooftop rainwater harvesting is concerned. So as we have already seen depends upon how much is the area, how much is the rainfall and how much is the collection efficiency. So based upon these three important aspects some of the design considerations I have listed here. So first one is area contributing for runoff so that means the harvestable rooftop catchments of the area then rainfall pattern for the area. So whether it is 4 months or 8 months or how many months per year and how many days in a year and then what is the intensity of rainfall and then collection efficiency. So as I mentioned whether it is say we can achieve about 80% in as far as rooftop rainwater harvesting is concerned and but when it goes to say open space it may go to 50 to 60% and then in say watershed based say rural rainwater harvesting is concerned it may be 30 to 50%. So like that say the collection efficiency varies then demand for water and type of use. So say in especially arid and semi-arid regions say where the rainfall is very less then whatever rainfall is there we can go for harvesting it and then we can say improve the waterivity. So this is a typical examples what is done by Mr Rajendra Singh in Rajasthan villages many of the Rajasthan villages where mass river rainwater harvesting is done so that the say even for arid regions or semi arid regions we can make it the waterivity better. And then another important aspect is the type of use. Type of use means whether the water which we are harvesting say especially rooftop rainwater what we are harvesting whether it is using for domestic purpose like drinking and other purposes or whether we are using only for agriculture purposes or for we charge purposes. So like that depending upon the type of use we have to have better schemes say for example if we are going for the say domestic purposes then we need the pure water. So that way we have to go through cycle of say filtration then say disinfection either to using say chlorination or ultraviolet systems and then maybe we have to again further go for boiling. So like that depending upon the type of use the design considerations will change. Then another issues say for example in a city like Mumbai where we are having rain for 4 months then say we can decide for how many more months we want to either store water for the dry months by period. So we have to decide for how many months we have to go for storage. Then storage related issues so as I mentioned whether we are going to store in say tanks like ferrocement tanks or a syntax tanks or what kind of tanks so depending upon that we have to do the design. Then we have to see the water quality issues. So as I mentioned say if the roof is concrete then the water will be much better but if it is aspectos roof we have to be very careful. So like that the quality of the water available what is harvested that also we have to take care. Then what kind of maintenance we have to go for the particular system that depends upon the design. So whether we go for a very good design with all the aspects then the maintenance required will be say maybe once in a year or 2 times in a year. But if the design is poor maybe weekly basis or mandatory basis we may have to do the maintenance. Then say as far as recharge is concerned when we are designing a recharge structure then we have to see that hydrogeological aspects so that how much water can be put to the aquifer system through various schemes like recharge pit or tube well or bore wells. So this depends upon the hydrogeology of the area. So then recharge structures is based on the recharge structures are based on availability of space, availability of runoff, depth to water table and lithology of the area. So these are some of the important design considerations as far as rooftop rainwater harvesting is concerned. So now as far as design criteria say if we are going to do a recharge for a particular area then we have to see the various aspects then say the runoff should be assessed accurately for designing the recharge structures and then may be assessed by the following formula which you have already seen runoff is equal to catchment area and runoff coefficient into rainfall and then runoff coefficient plays an important role in assessing runoff availability and it is and depends on upon the catchment characteristics. So this issue we have seen in the last lecture so depending upon the type of catchments the runoff coefficient varies say for example depending upon the type of roof this can vary from 0.7 to 0.9 and then paved area it can vary from 0.5 to 0.85, bare ground 0.1 to 0.2, green area 0.05 to 0.1. So like that this runoff coefficient can vary from area to area. So now say when we are going to especially for recharging the aquifer system so we have to design the specific recharge structures so we have seen various structures like whether it is a recharge pit or recharging trench or say borewell or dugwell so like that. So the cost depends upon various conditions so like that the locality the that means in cities the cost may be more in rural area cost will be less then say what kind of soil or what kind of geological nature as far as when we are making a pit or a trench. So the cost of each recharge structures varies from place to place say some of the approximate cost I have listed here so like recharge pit it may vary from rupees 2500 to 5000 recharge trench vary from 5000 to 10,000. So like that say this is I cannot specifically say that this will be the the correct cost as far as a structure is concerned so this varies from location to location and then depending upon the soil geological and other parameters. So now within this perspective within the issues which we have discussed so now let us see how we can do rooftop based rainwater harvesting system. So we have already seen there are mainly three components one is the rooftop catchments so that what we are say through which what we are the rainfall what we are collecting so that is the rooftop catchments and then that is the first component then second one is the collection. So if this is the building then the top of this is the the the catchments and then collection is we have to collect the water through gutters and then through pipelines. So this is the collection systems so that is the second component so first one is the catchment second one is the collection system through pipelines and then third one is the storage system. So if you are going for direct say storage then a tank like this is a ferrocement tank so what is the size of the tank and various other say aspects of design of the tank so like that mainly three components one is the the catchments collection system and the storage system. So this is as far as the catchment area so as I mentioned it is mainly the roof so the catchment area is the surface through which the rainwater runoff is harvested that is a roof so water to be used for non bringing purpose can be collected from any type of roof so if you are going to recharge the to the aquifer system of course the quality of water should be good but say for example if you are going to use that collected water for irrigation purposes then we do not have to worry much so we can collect the water from any kind of roof. Then water to be used for bringing purposes should however not be collected from roofs with a damaged aspect of sheets or from roofs covered with asphalt and lead flashings or lead based paints as lead contamination may occur in the collected water. So say whenever rainfall takes place it is pure water but when it say where it falls depending upon the roof type so the contamination can take place say for example if it is asphalt say covered roof or aspect was roof then many components like lead lead or other ameters can say mixed with the the rainwater so that will lead to contamination so we should be careful so what kind of say roof which we are having and then accordingly we have to decide whether that water can be used for domestic purpose or only agriculture purpose or say to to recharge to the aquifer system. Now regardless of the roofing material generally a loss of up to 20 percent may take place due to evaporation inefficiencies in collection and inefficiencies in collection processes. So there is only generally about 80 percent of rainfall can be harnessed through the roof top catchment system so that is generally approximately we can collect about 80 percent of the rainfall say what is coming on the roof top. So now say second come on in this say we have to collect this water from the the roof and then we have to send through appropriate system so either for say storage in a tank or for recharge purpose. So that the inflow the inflow structures are important so some of the important info inflow structures include gutters so this gutter so it is generally on the say on the side of the roof so that this gutters collect rainwater from the roof and transport it to the inflow pipe. So you can see that whatever is collected so that will be coming through this pipe. So the gutters could be of various shapes and shapes sizes and materials so like aluminium or say PVC type different types are possible as far as gutter is concerned. And then say once the water is flowing through the gutter then we have to collect it through pipe so that is called inflow pipe so that this is the inflow pipe or this is the inflow pipe coming to the storage tank. So this is the from the gutter water is coming and then coming through the pipe here. So inflow pipe or drain pipe is the pipe which connects the gutter to the filter and then to the tank or to the reservoir. So the inflow pipe say design you have to do appropriately so that you can see that if this is water coming through this is the gutter so where the water is collected and from the gutter now water is entering to the through the pipe so that now that will be coming to a filter or other kinds of system. So the inflow structure structures are very important so we have to design it appropriately. So from the pipe say inflow pipe that may the water may go through a filter and then that can be either used for storage or for recharge purpose. So now as I mentioned the filtering is very important since even though say the first say the first rain first 2-3 rains we can flush it out but still there will be especially in city regions there will be dust and then lot of other bedrope and other things as far as the roof top is concerned. So a filter is always needed even if we are going for recharge purpose. So a filter is to be used when the water is to be stored in tanks for direct consumption or whether even if it we are going for recharge. So we can see that say different types of filters are available. So you can see that water is collected and through the collection system what is coming to a tank where the filter material is put. So this is the inflow pipe so here this is a typical say filter material is put. So here the this is the filter wall and then fine to coarse sand is put on the top then gravel and just below that and then pebble below that. So from that now say after the filtration the water will be collected to the tank where the water will be stored for either direct use or for recharge. So you can see that this filter can be either of this sand material or the gravel and pebble material like this or we can nowadays in a compact form the filter is available. So like say for example but now the scheme here we can have a module say here this is a module which is put in the collection pipe itself say like geotextile or PVC type material various materials are available nowadays. So through which water will be passing for storage. So here you can see that say this is now the water is coming and then now the flush valve and then the water will be going through the filter system. So now say when we design the rainwater harvesting as I mentioned the first flush first 2-3 flush first 2-3 rainfall flush should be should not be allowed to collect or it should not be allowed to recharge since it contains lot of dust and other pollution. So what we can do we can have a valve here so that say during the when the monsoon or when the rainfall comes we can close this valve and so that first 2-3 rainfall is consents the all the collected water will be going through this pipe out. So that will not be collected at all. So that is we consider polluted water and then after 2-3 flushing say removing this say the water coming from first few rainfalls then we can close this valve towards this and open towards the tank so that the water will be passing through a filter system and then that can be used for storage in tanks or we can use it for the purpose of recharge. And now so that is say that is the way the design is done. Now say if you are going to recharge the groundwater the water to the groundwater reservoirs then for storage in groundwater reservoirs the filter in the inflow structure say a very good filter is not required but of course we need to it should go through somewhat a small filter or a sedimentation process. So the water however should pass through a desiliting pitch before entering the aquifer system. So you can see that this is our dug well through which we are going to recharge. So the water is coming inflow is coming like this and there is a desiliting pitch and through which the water the silt all these things will be set in down here and then the pure water will be allowed to go to the dug well where it is allowed to recharge. So either we can give a filter or we can give a desiliting pitch like this. So that the suspended material settled down before the water is introduced to the aquifer system. Except for the recharge through hand pump or tube well the filter should be constructed. So if a filter to be given we can give a filter somewhere here say maybe after desiliting so that the filter water will be allowed to recharge to the aquifer system. So now say we have seen say water is coming from the catchment I mean roof catchment through the collection pipes and then after filtration or desiliting we can use the water for the purpose of storage or for the purpose of recharging. So if you are going to recharge the recharge different say we can use recharge shaft say different different bore wells trench with injection wells so like that. So this is this is a trench and then there are two injection wells within that trench and that will be allowed to recharge the aquifer system. And now also if you are going for collection tanks say for example you can see that now the before the once you start this tank will be clean then the water will be coming through to the tank and that will be stored. Then we can have a pumping mechanism here through which water can be pumped for the purpose what is then what we are using for. Underground tanks are designed and constructed in such a way that there is no leakage so we have to take care so that the tanks can be either reinforced congate, perocement or PVC type tanks. So that way depending upon the money which can be spent and the space and then the design consideration we can use particular systems. So now say as far as storage is concerned so as I mentioned we can have storage tank and then we can say use allow the water to go through the recharge wells dug well abandoned dug well or recharge well or recharge shafts or recharge trench. So you can see that we can have trenches surrounding the building like this and then also we can abandon dug well this is a scheme and then this is a recharge shafts. So here with this water will be say allow to recharge to the aquifer system. Now let us see what is the cost of rooftop based rainwater harvesting system. So as I mentioned the cost depends upon the location and then also depending upon what kind of design we are planning to do. So we can have very good design where the cost may be slightly more or we can go for what kind of say it depends upon how the how much money we can how much capital is there. So the cost of rainwater harvesting systems designed as an integrated component of a new construction project generally it will be low. So now a building is already constructing then in that process if we are planning in advance a rainwater harvesting a rooftop rain based rainwater harvesting system then we can do all the arrangements then while doing the construction itself especially plumbing itself. So that there is the all the say the rains coming from the roof can be put it appropriate way so that that can be our collection systems. And designing a system on an existing building is costlier since say if an existing building there is no effective way of collection and say collection of the rainwater then we have to have a new system to be developed. So because many of the shared cost like roof and gutters has to be separate as far as the old building is concerned. In general maximizing storage capacity and minimizing water use through conservation and reuse are important rules to keep in mind. So say we want to maximize storage and minimize the water use so that way we do the cost analysis. Now with careful planning and design the cost of a rainwater system can be reduced considerably. So we can say we have to do a preliminary analysis of the site and then we have to see how much rainwater is possible to harvest and then say we have to design the system appropriately so that an appropriate design can reduce the cost considerably as usual for any kind of design is concerned. So now say the rainwater harvesting methods are site specific as I mentioned hence it is difficult to give a generalized cost. So this depends upon the location and many other parameters. But first of all the major components of rainwater harvesting system like rain and catchment area are available free of cost so which is the most important aspect that is the initially there is no need of a capital as far as rain is taking place naturally and then you are having already the rooftop as the catchment. So these are already available free of cost only we have to go for the collection system and then we have to go for the storage or the recharge system. So a good proportion of the expenses would be for the pipe connections as I mentioned especially the collection of the rainwater and then of course storage. So by judiciously fixing up the slopes of roofs and location of rainwater outlets this could be brought down considerably. However cost varies widely depending on the availability of existing structures like wells and tanks which can be modified and used for water harvesting. So if there are tanks are available and then or if some dug wells are available which we can use for the artificial recharge then the cost can be considerably reduced. Typically installing a water harvesting system in a building would cost between say 3000 to 50000 for building of about 300 square meter. So this is a say an approximate rate as I mentioned it varies from location to location. So it varies say it can be generally between 3000 to 50000. The cost estimates above is for an existing building. So this is for an existing building. So when we are doing it for a during the construction then the cost can be again can be reduced. Say for example rainwater harvesting system in the the centre for science and environment building daily was set up with the cost of 30000 rupees whereas those in the model projects say other projects range from 70000 to 80000. So this drastically varies from location to location. Then the cost would be comparatively less if the system were incorporated during the construction as I already mentioned. Then when community come together to harvest rain per capita cost goes down. Say for example if there is a housing colony. So colony wise when we are going for total rainwater harvesting system then the cost can be considerably reduced. So since the same scheme can be adopted by all the housing houses in the colony and then even recharge pit we can have common recharge techniques or filtration is concerned we can have common system. So like that the cost can be considerably reduced. Say for example for punch shield park colony in New Delhi about 1000 residents pulled only rupees 4.5 lakhs to harvest more than 170 million liters of water annually. So you can see that say 1000s residents came together. So the cost has gone drastically down and then there is a much better rooftop based rainwater harvesting system especially say in Delhi area they went for recharging system. So now say these are as far as these are the issues as far as the costs are concerned. Now let us look say some of the safety considerations as far as the rooftop based rainwater harvesting is concerned. So if you are going to store water in a groundwater reservoir so then for rooftop rainwater harvesting through existing tubulars and hand pumps the filter or desilting pit should be provided so that the wells are not silted. So the existing if you are going to harvest the water and then put to the aquifer systems through existing tubulars or bore wells then you should be careful. So it should be passed through say filtration is essential. So that the existing wells are not silted. Now such tubulars if pumped intermittently increase the efficiency of recharge. So it is not only recharging through the system intermittently we can pump out also so that the efficiency of recharge will be increased since somehow the silt will be coming out. Then if the groundwater reservoir is recharged through shaft, dug well etc. inverted filter may be provided. So here we can see a system where the water collected and after the sedimentation the water is going through a pipe through a filter and then this is connected to an existing tubule where this tubule says sometimes used for say pumping also and whenever excess rainfall is coming water is coming then that is used for recharge purpose. So both dual purpose tubules this is a dual purpose tubule. So otherwise we can construct structures like this. So now instead of recharging say if you are going for storage in tanks some of the important safety consideration which we have to adopt as far as a roof top based grade mart harvesting is concerned. A storage tank should not be located close to a source of contamination such as a septic tank. Then a storage tank must be located on a lower level than the roof to ensure that it fills completely. Then a rainwater system must include installation of an overflow pipe which empties into known flooding area. Excess water may be used for recharging the aquifer system through dug well or abandoned hand pump or tubules. Then you can see that most of the say wherever high intense rainfall is there then the flow through the collection pipe will be much higher. So we have to give a speed breaker plage that is provided below the inlet pipe in the filter source not disturb the filtering material. So if the water flow to the filtering material is velocity is very high then the filtering material will be affected and that itself will be going through with the water. So we have to provide some speed breaker. Then a storage tank should be accessible for cleaning regular cleaning is required say before months soon definitely one cleaning is required and then depending upon the recharge or depending upon the use we may have to clean that tank say the storage facility. Then the inlet into the storage tank should be screened in such a way that this can be cleaned regularly. Water may be disinfected regularly before using for drinking purpose by coordination or boiling. So these are some of the important safety consideration as far as the rooftop based rainwater harvesting is concerned. Now some of the operation and maintenance issues here I have listed. So proper operation and maintenance is required. Regular inspection and cleaning of catchments, gutters, filters and tanks reduce the likelihood of contamination. So that is an important point and water from the source should not be mixed with that in the tank. So other sources like if the water supplied through pipes that should not be mixed with the harvested rainwater. Then as far as treatment is concerned treatment of stored rainwater only makes sense if it is done properly. If hygienic collection and use of water will ensure and it does not suffer from recondamination. So recondamination should not take place we should be careful. And there are several types of treatment possible like chlorination boiling in filtration and then expression provided natural sunlight etc. So these are some of the operation and maintenance aspects as far as rooftop based rainwater harvesting is concerned. Now before going to case studies let us have a look some of the water quality issues. So to prevent leaves and debris from entering the system mesh filters should be provided especially at the mouth of the drain pipe. Then as I mentioned the first flush defy should be provided in the conduit before it connects to the storage tank containers. So if the stored water is to be used for drinking purpose then a sand filter is essential. Then methods to protect rainwater quality include like appropriate system design sound operation and maintenance. Then it is extremely important to maintain the rainwater harvesting system regularly for high quality performance. So the quality depends upon the maintenance of the system. Then some of the tips to ensure good quality of harvested rainwatering would just before the arrival of monsoon the roof prop and catchment should be cleaned properly. The roof outlet to the stairs should be covered with mesh to prevent entry of leaves and other materials. Then the filter materials have to be either replaced or washed properly. Then the diversion valve has to be opened to the first 5 to 10 minutes to dispose the polluted first flush. The no polluted water should be taken away from the richer structures and then the depth of bores shall be finalized depending upon the actual site conditions. So these are some of the water quality issues. Now say here say if you want to design this is a simple problem say a rainwater system has to be designed for meeting and drinking water requirements for 5 member family in a building with a roof top of 100 square meter average annual rainfall in the region is say 600 mm daily drinking water requirement per person is considered 10 liters. Then here we can see that catchment area 100 square meter rainfall is 0.6 collection efficiency 0.8 then we can find the average annual water harvesting is 48 cubic meter. So then say if you consider say for example about 240 days of dry period then we can identify how much is to be collected for drinking purpose. So then if you give 20 percent extra then it can be 14400 liters. So we have to design accordingly. So two case studies here I want to present one is the success story of as far as artificial recharge is concerned. So first one is artificial recharge ground water using roof top. So this is the Shakti Bhavan in New Delhi. So the the canvas area is about 12000 square meter depth of ground water before recharging was 68 meter below ground level. So here this is the system so you can see that various through various pipelines are collected and then they through two injection wells and recharge trench the water is infiltrated down to the kiffer system. So average annual rainfall is about 712 millimeter. Rainwater runoff approximately calculated 3,325 cubic meter. Structure proposed is recharge trench with the two injection wells. Aspect of recharge is about 3000 cubic meter per year. So the studies in 2007 shows that there is about 1.68 to 3.33 meter rise in the area in the on water table and cost of the water was calculated as rupees 7.07 per thousand liter. So the total cost when it was implemented by Central PWD in 2001 was about 4.1 lakh. So major benefit proper utilization of available runoff arresting the declining ground water levels in the area and sustainability to existing ground water abstraction structure. So this is a recharge based case study. Second one is a collection type case study. So this is in Mumbai Indian Water Works Association campus. So here the storage is done in a ferro cement tank of about 6000 liter and Mumbai rainfall average is 2335 millimeter. The rooftop area is about 300 square meter. So the design is based upon this data. Then filter material is here. This is the collection system. This is the filter material, the geotextile based system and then the overflowing water for recharge say water is collected in a tank like this. So this water is used for toilet flushing as far as the building is concerned. So this water was found to be sufficient for months and months plus and then one month after the rainfall. So one month rainfall storage and they could do and the cost was about 96000. So this is another efficient direct rooftop harvesting as far as storage is concerned. So for today's lecture some of the important references are listed here. Then as a tutorial question say two questions I have put here describe the artificial recharge scheme for groundwater improvement with case studies. Illustrate the rooftop water harvesting with the help of two case studies for direct use and groundwater recharge. So you can see number of case studies in Central Groundwater Board website invertharvesting.org website and CS India website. So you can illustrate the system with various schemes and then discuss various techniques adopted and discuss the merits and demerits of each system. So if you self evaluation questions like discuss the rooftop rainwater harvesting then needs and its importance. How much water can be collected from a rooftop catchment? Discuss the important design consideration of rooftop rainwater harvesting system. Discuss the cost analysis of rooftop rainwater harvesting scheme describe the operation and maintenance of rooftop rainwater harvesting systems. Then assignment a few questions describe the methodologies of rooftop rainwater harvesting system. What are the solution strategies for urban rainwater scarcity? With the details explain how we can do rooftop rainwater harvesting. What are the important safety consideration in rooftop rainwater harvesting and discuss water quality issues in rainwater harvesting. So these for the answers for all these questions you will get through if you go through the through today's lecture. So finally one unsolved problem for your residential building where you are staying to prepare a master plan for rooftop based rainwater harvesting system. So you can identify what is the present supply water is coming from where and what is the demand for the your building then you can identify the built up area and check the possibility of direct rainwater harvesting or you can go for recharge. So collect all the data, let it rain falls, soil data etc. Then design an integrated rainwater harvesting system including some storage in tanks or some say the option for ground water recharge. So with this today's lecture on say rainwater harvesting especially rooftop based catchment system is finished. So now the module number three on the integrated say watershed management schemes also over. So we have see we have got about four lectures in this module on introduction to integrate watershed management. So various aspects of the scheme the this module has been discussed in the four lectures as we have seen the last four lectures. Thank you.