 So, getting back to the topic again this is the outline slide we saw the water cycle, we saw the water problem in all its various dimensions and then we also started looking at some of the solutions in which we looked at rainwater harvesting and how that is useful and very important to do. The now we are going to also talk about something that is again equally important particularly for the rest of the water that we need. So, the rainwater harvesting was mainly in the context of providing adequate drinking water although rainwater should be harvested for more reasons than just drinking water. So, taking it further now how do we ensure that enough water is made available for all the other requirements and in that we need to connect back to the water cycle that we studied. In the water cycle we studied that you know there is evaporation that happens from the oceans and all many other surfaces as well it goes as water vapor which forms clouds and then there is precipitation and in India there is more rain than snow. So, it falls down as rain and then it flows over the surface in the form of streams and rivers and back to the ocean, but some of it percolates underground and then underground it follows a much slower pathway to reach the ocean again. So, the part of this entire hydrological cycle that is useful to human beings in which the water remains of direct use to human beings is from precipitation to the point that the water reaches the ocean. The rest of the part of the hydrological cycle is not directly accessible to us we cannot directly get water out of that. So, if at all we have to make any alterations modifications then we can only do it from the point of rainfall until the water flows to the sea. Now, I had made a passing mention before that in India we have a monsoon climate where roughly 80 percent of the rainfall happens between the monsoon months which are June to September the southern tip of India has another return monsoon sometime in November December, but for the most of the subcontinent this is the situation. So, if we manage so actually 80 percent of the rainfall in just a few months is actually very difficult for us to ensure adequate water supplies throughout the year. So, you have all the rain that simply flows over the surface and reaches the ocean and then the rest of the year you are left with none. So, there is a it is of great importance to ensure that the water actually remains available for the rest of the year. So, that can be done by what is known as watershed management. So, let us first try to understand what a watershed is and I am sure that many people might have studied this concepts in school, but again the reason I have put these things and I think somebody in the chat had left a message that this is relevant only to school children and not to engineering students. I do not subscribe to that idea because I have observed in many of my classes students have very little recollection of whatever they must have learnt in school. So, if I start off at assuming if I start off assuming that they already know this terminology and everything it does not work out. So, I invariably have to end up going to relatively basic concepts. So, I do not think there is any harm in doing that. If you feel that your class is actually at a much higher level then you can modify your approach accordingly, but I think it is more common for students to not remember all these things even if they have done it in school. So, let us start by understanding what a watershed is. The watershed is that region of the land where the water that falls on it as rainfall will all drain down to the same point be it the ocean or be it a lake or be it some other water body. So, the watershed contains various streams, it may contain rivers or rivulets which all converge to the same point. So, if you look at this diagram there is a maybe it is not very clear, but there is a dotted line over here. So, any rain that falls on the left of that dotted line that is on the other side of the ridge would be part of a different watershed. Any rain that falls on the right side of that dotted line would be part of this watershed. So, that is the idea of the watershed it is that trough like area where wherever you wherever you pour water it will all go and converge in the same place ok. So, now these watersheds smaller watersheds are part of larger watersheds. So, maybe the watershed of a small tributary is part of the watershed of the major river into which that tributary merges. So, you have these some of these watersheds which are very very large and they span across states and you have even cities that are included in that. Now, since there are cities and roads and everything that are included in the watershed, there are so many sources of pollution that are there within the watershed. And so, the water along as it flows carries maybe some soil eroded soil maybe some sediments and pollutants as well. Now, as I said if you have rain only in 3 or 4 months during the year and all that rain is going to fall on that land and it is going to drain right into the river within a few days it is going to reach the ocean. So, you can depending on which river is nearby you can calculate the distance from the ocean and you know assume some reasonable number for an average velocity of water and you can calculate how many days it is going to take for the water to reach the ocean. And typically in many places it would be a matter of days not much more than that for the water to just be lost. So, the water that goes back into the ocean is not usable for us. Whereas, if you if the water on the other hand if it percolates underground then the flow is much much slower and the water may take months years or several centuries to reach the ocean. So, if the ground water flow is much slower and during the entire time that it is flowing slowly underground you can always tap it by digging a well or a bore well. So, there is a benefit in ensuring more ground water recharge as opposed to surface runoff. This may sound very simple, but if we merely succeed in doing that I think our countries water problems would be a lot less severe. So, how do we ensure that that the water does not get lost within a matter of days after precipitation? So, good practices good management practices throughout the watershed can actually enable this to happen. In that I want to emphasize the role of plants and natural ecosystems. If you in your course you might be teaching topics on ecology and biodiversity. So, this is a good point where you can relate some of the things learnt over there the need for preservation of natural ecosystems. This is a direct reason why we should preserve these natural ecosystems. So, let us see how plants and natural ecosystems benefit the flow of the management of water in the watershed. So, if plants are not present the raindrops which fall from the sky you know as they are released from the clouds they are falling at a terminal velocity which depending on the droplet size may be between 7 to 30 kilometers per hour and that can be quite a significant impact on the soil. So, when you when that raindrop hits the soil directly an uncovered soil you see a kind of a miniature explosion that you that happens on the soil and soil particles can be ejected upward and horizontally to quite some distance. So, that impact actually causes lot of damage to the soil the soil loses its structure and it starts the process of erosion. On the other hand if the soil is vegetated if there is some vegetation on the soil be it grass or be trees if there are trees there will be some ground litter fallen leaves dead leaves. So, all this together there the trees will intercept the raindrops at the canopy the rain rain water will trickle down fall on the bed of leaves and it will trickle down further to the to the surface of the soil and the soil damage is prevented. So, then again you know if there is vegetation on the ground it the water that is flowing over the surface the surface runoff velocity also is controlled which again limits sheet erosion. The roots of the plants will hold the soil tightly and prevent further erosion and loss of soil. Now, when you have vegetated soil with roots inside the soil it is living soil. So, there are creatures that are present in the soil which are making burrows into the soil making sure that the soil remains porous and aerated. So, when you have these burrows in the soil it in and the porosity of the soil is high naturally it allows for more percolation of ground water underground. So, instead of having an impervious layer of hard soil over which most of the water is going to runoff now you have a sponge like soil which will absorb some water and encourage percolation. So, when water actually percolates underground it is following the slower path to the ocean in which it remains usable for a longer period. So, moreover the plant plants growing over that add humus to the soil which improves the soil fertility and its productivity and many plants even fix nitrogen. So, you have better productivity out of the soil. Now, so when you have less erosion and you have less damage to the soil the silt load is also reduced. One problem that many dams are facing today is that the dams silt due to erosion from the hill slopes. See when there is deforestation in the catchment of a dam the catchment is that part of the water shed which is above a dam upstream from the dam. So, in the catchment when there is a lot of deforestation trees are cut the hill slopes are burnt many people burn these hill slopes to clear the vegetation and to ensure that they get good grass in the following season. But that leads to lot of erosion right after the rains and all that soil that silt that comes along with the water goes and collects in the dam. So, the dams reservoir capacity reduces. The benefits that the dam was going to give during its lifespan also reduces its lifespan reduces. So, again you have to go for desiliting of dams which becomes expensive. So, that is an additional cost. So, in the in the lifetime of the dam the cost-benefit ratio is very adversely affected. So, if the soil is vegetated then the erosion is reduced and during and the soil also becomes quite productive. So, I have the all the points that we just now discussed I have summarized them in a table where we compare barren land versus vegetated land. So, you see that direct impact of raindrops on soil on barren land yes you have direct impact and on vegetated land you do not have direct impact. So, all these points like loss of soil structure and erosion in barren land you have it in vegetated land you do not this is just for some easy reference ok. Now, so the most important thing to do in a watershed is to ensure adequate vegetation natural habitats if they are preserved then naturally you have taken the first step towards ensuring good water supplies. If you have deforested hill slopes in the watershed then you have taken the first step wrong. So, then after that what follows is that the water that is then flowing downward in the watershed we must try to slow it down because as the water flows faster it has more kinetic energy it can lead to greater erosion. So, we have to slow it and we have to store as much as possible. So, this can be done by making surface tanks or we can make percolation tanks which are like small ponds, small bunds and things like that there are various structures which I am going to show you a nice video for. The extraction of ground water again has to be limited because if you over extract then it is going to deplete the aquifer and an aquifer is shared by a large number of people it is possible for one or two entities to over extract water and inconvenience a large population. For example, a large possibly a cement plant or a thermal power station can you know over extract resources and or some agricultural age area you know they can over extract water and they can deplete the aquifer which adversely affects everybody else. Now, instead of going through the various structures the engineering structures that are normally made or followed in watershed management. So, we are trying to make more water available for people. So, that is done by slowing down the flow of water after precipitation and trying to store it wherever possible. So, it all starts with protection of vegetation in the catchment. So, that is control of deforestation, control of over grazing and of fire. Then if there is a slope the water tends to flow and gather speed as it as it flows down. So, it is better to terrace the slopes so that the water kind of slows down over there and at the periphery of the terraces or along contours they normally dig trenches and they put the soil on the downward side. So, it forms kind of a bund and those bunds can be planted with some plants or some trees. So, these are planted bunds. So, there is a trench and a bund. So, the water that flows goes along the terrace slows down then accumulates in the trench and large amounts of the water tend to percolate underground and recharge the ground water rather than flowing on the surface. Then there are small tanks that are constructed, there are bunds that are made percolation tanks. There are in places in where there are streams they make check dams to reduce the velocity of water. So, large amount of the silt actually gets intercepted there itself rather than going to the larger bunds. So, there are various practices that they follow and this can make a lot more water available moreover in the watershed it is important to minimize the wastage of water. So, that includes choice of crops. So, if a certain region has got less average annual rainfall then insisting on planting a water hungry crop like bananas or sugarcane or coconuts is is not a good idea at all and in fact, it will end up depleting the ground water. So, the choice of crops is also very important and then the crops that are planted should be based on the seasonal availability of water. So, planting something in summer is probably again going to deplete the scarce ground water resources. So, when all these things are done then you will find that quite contrary to the situation of large dams where the people whose land gets submerged, they bear the costs, they do not get any benefits of the dam and people downstream in the command area of the dam they get benefits from canals and hydroelectric power and what not. So, in contrast over here in watersheds the prosperity that is associated with this project is distributed everywhere more or less evenly. So, because even in the in the upper reaches of the river system you have small dams and structures where people have it is at least adequate for people to do their agriculture and their basic meet their basic needs. One issue though is large dams produce a lot of hydroelectric power and these smaller smaller dams or medium sized dams they do not produce as much. But if the provision of energy in a watershed is looked at in a comprehensive manner then by integrating other renewable forms including wind turbines, solar and micro-heidel or mini-heidel projects all together it may not be such a bad deal compared to a large dam. So, there is another very important point is that these watershed management programs they will not succeed if there is no community involvement. So, there should be education of the community awareness creation for the community, there should be empowerment of the community. So, the community should run the project themselves it is not if you are expecting the government to do everything it will probably not happen in the best possible way and the funds might simply get wasted. But when the community takes ownership of it and they contribute their labour also and they ensure that it is done then it can actually be successful. There are really amazing success stories in this area and I am going to show you the video of this place called Hivare bazar where there was it was a village like many other villages where due to scarcity of water and rampant crime and alcohol problems and other gender related issues it was a probably a horrible place to live. But due to the initiative taken by the villagers over there it has now completely it is now a changed place and the village boasts of something like 52 millionaires in that village. So, that is so good to know. So, let us watch this nice video. So, I hope you like this video there are there are several such places in India several environmental heroes, social heroes in I mean they are around every corner we just do not happen to see them and I think you know I think media gives too much attention to the problems that we have maybe some attention is required even here to appreciate their efforts. What a wonderful work they have done and there are there are other examples at Radegan Siddhi also I have personally visited many many years ago and I was really impressed by what all has been achieved over there that that again is a similar place where rainfall is low and all these problems that they talked about pretty much used to be there until Anna Hazare came over there and did what he has done. So, I think it is important to identify local examples so that it impacts students in a bigger way, but at the same time showing some examples from across the country is also useful. I just I had made a mention of how for centuries people have been people have developed very nice methods of conserving water of storing water in various parts of the country. This kind of lists down some examples and this is not comprehensive at all. So, you can feel free to add more to this and do make it a point to discuss these things with your students so that we actually learn together. There is another activity that you could probably do with your students and that is to identify which watershed you belong. I am sure your city or village or town wherever wherever you are located is part of some watershed. So, it is a good idea to try to identify which watershed you belong to and then classify whether what type of a watershed it is and what are the major issues in that watershed. You can identify some government agencies to get this information or some non-governmental organizations and then when you know that there are some issues maybe you can contribute in some small way to towards the various efforts for restoration of the watershed by forming the citizens groups or even through your nature clubs. I think most colleges will certainly have nature clubs. So, once we have adequate water available how do we then maximize its benefit and how do we use it efficiently. So, that is the second part. So, in the first part we decide we we made sure that adequate water was made available and then in the second part we are going to see how to use it efficiently. So, let us look at why we need all that water. So, we need water for three major end use sectors that is agriculture, industry and domestic consumption and the numbers are roughly as seen on the slide is there agriculture is roughly 87 percent industry is about 8 percent and out of that 8 percent 7 percent is for thermoelectric generation. So, the 1 percent is for rest of the industry and domestic is mere 5 percent. So, I put in the reference over there so you can you can refer to that source. So, once we get an idea of where the water is actually required you know then we will know we can think better of how to use it more efficiently. So, if 87 percent of the water that we extract from all the various sources is going for agriculture then we right away we notice that water agriculture food and waste they are all inseparable they are very closely related and they should be considered together to evolve solutions. And again I am I am repeating what I have said before that more than 50 percent of the food comes from the irrigated land which is only 35 percent of the land and we have roughly 30 percent of degraded land. So, what can we do then we can actually we need to develop organic polycultures or agro ecosystems which are water efficient they are low input. So, agriculture requiring too many inputs be it in the form of irrigation or being it be it in the form of fertilizers and other agro chemicals is not going to work out in the long run because of the environmental impacts. And I am going to discuss a little more about that in the in the topic on food on Friday I believe. So, what can really revolutionize this area is low input organic polycultures by polycultures I mean different species of crop plants grown together which can which can provide high yields and at the same time not require so many inputs the more the inputs the agricultural system requires the greater are the environmental impacts. So, there are there are cases where the yields of rain fed lands can increase from between 15 percent to 150 percent in in these low input organic polycultures. Now, it does not mean that they will always over yield compared to the previous methods, but if designed well they can they can give very high yields. Now, inputs of organic carbon waste to the soil can improve not only the productivity, but it can also reduce water use because organic carbon in the soil makes the soil hold more water. So, it means the irrigation requirements are somewhat lesser. So, carbonaceous waste all the organic waste that comes out of our our kitchens or from from dairy animals and things like that can be composted and if the compost is added to the soil then the requirements of fertilizer also reduces and the solid waste also reduces in volume. I think depending on the place it would vary, but for the solid waste I think nearly 50 percent of it would probably be organic and compostable material and could be as I said you know depending on whether it is urban or rural and in various places it would change a bit, but it is I think in general maybe safe to assume that it is at least 50 percent in India. So, what do I mean by these polycultures? There is a I want to I am debating whether I should show you this video on Friday or today. So, this is a 300 year old agro ecosystem it is a food forest in Vietnam. So, it is a forest which looks very much like a forest, but it has all food plants and it has been around for about 300 years with a with a family. The beauty of this of this food forest is that it does not yield only in one layer. So, let us take the example of a rice field or a wheat field. You have the rice or the wheat that grows in a certain area and you know that is the only layer that is yielding, but in a food forest right from the underground layers which is tuber crops. You have tuber crops as well as vegetation that grows close to the ground, then you have the herbaceous layer, then you have the creepers and the vines, then you have the shrubs, the short trees, tall trees, some seven layers in in these food forests each layer giving some fruit or some useful product to us. So, it could be yielding either food medicine or fiber like like cotton for instance. So, it could be or maybe wood. So, there are these various outputs that come from these food forests and they these outputs are derived from various layers within the food forest. So, as a result these these food forests can be enormously more productive than our conventional systems. The beauty of such such arrangements is that these are perennial systems you do not. So, if they are perennial systems it means that every season you do not have to plow the soil. If you do not have to plow the soil and add fertilizer and add tremendous amounts of labor every season I mean that increases the costs. So, this is low input or almost zero input because the seeds fall and new plants again sprout up over there. So, this is a completely different way of thinking about agriculture. These are enormously productive. So, we are not taking a hit in productivity and again these are so resilient that they have this particular example that I am showing you is has been around for 300 years without any problem. So, I guess we will go ahead and watch this video. So, we are back I will discuss a little more about such systems and in the in the talk on food later. But I want you to appreciate one thing you know I would like to remember something I had told you in the topic on sustainable development where sustainability requires a coordination from different fields. So, this is something that you see over here there is it is a food forest, but it is also a gene bank. He mentioned about people coming to their food forest and asking for their genetic material because they are immensely productive agro ecosystems and that genetic material is extremely valuable. So, not only are they getting food in a very efficient manner, but they are also producing they are also maintaining a gene bank a living gene bank of these materials. Again all those things about water conservation since you have trees there is the canopy interception recharge of the ground water all those good things are happening. Then again the inputs are so less because it is well shaded there are trees which strike deep roots and because they have deep roots irrigation requirements are very little and of course, it is Vietnam. So, it rains quite a bit over there, but such systems if you have in an agro ecosystem if you have tree crops then generally they are the trees require less frequent irrigation. So, the inputs are very less and the output is very very high. So, as a result the if you put the inputs in the denominator and the output in the numerator you will find that the inputs shrink to a very small number and the output being very high these systems are highly efficient. So, these are if we develop systems like this and they do not all have to look like this I think people from Konkan or Kerala they might they might have seen similar systems there are there are farms which are which actually have things like that in I have seen personally places in Konkan as well as Kerala which are similar. So, they do not all have to look like this I mean the species of plants can be different if you live in a in drier parts then obviously the species would be different. I have also seen an example of a similar food forest somewhere near Israel I do not remember it properly, but somewhere in the Middle East. So, they the species that they have are different, but you can still have similar structures again highly efficient perennial systems. So, you are not afraid of them dying out recently because of the hail storms in North India farmers suffered such terrible losses. Can you imagine a food forest like this if there is a drought for a year or a few years maybe the herbaceous layer may suffer some losses, but nothing is going to happen to the large trees if there is a thunderstorm or some rainstorm maybe one or two trees may fall over, but it does not destroy the forest. So, these are these are highly resilient systems. So, we need resilience we need resilient systems like that. So, there are many things these that can be done in this and maybe a little more will be covered in the food forest, but basically the concept of getting maximum output with minimum possible inputs. By inputs I mean it in a somewhat of a general sense inputs of water, labor, energy, all the inputs that go into agriculture we need to minimize that and get the maximum output and these such perennial systems are very they score very well on those criteria. So, that is about something about something we can do about agriculture which consumes most of the water then about industry rather than rather than going in detail about industrial wastewater management which probably many textbooks already deal with. I am just going to take a very superficial, but general approach where what I am showing here is various items that we purchase some of them are food products some of them are like t-shirts shoes and things other products they are they are all manufactured or they are processed in some industry and they require they require water for processing them. So, there is what is known as embodied water it is the water associated with that product which is with the water which was consumed during its production its distribution and maybe its end of life its disposal. So, 100 grams of potato has 25 liters of associated water which is the embodied water a pair of shoes has 8000 liters. So, what this goes to say is that when you shop you are placing a demand for water and if you shop for unnecessary items it is going to it is going to prompt more and more extraction of resources. So, just as there is embodied water there is embodied energy and we have an energy crisis also. So, when you shop unnecessarily when you buy consumer products and most of these consumer products maybe are discarded the same day or maybe within a few days or within a few months. So, for all for such a small use that they provide to us they you actually have to extract such large quantities of water as well as spend so much energy. So, conscious consumption is very very important reducing unnecessary consumption reduces the energy and water crisis. So, for industrial water use specialized treatment is required and in fact, again what we this is one point that we had earlier discussed is that we tend to create problems first and then keep ourselves busy in trying to solve them. I do not think that is a very intelligent approach. The more intelligent approach is to design our processes and our products so that we do not create a problem. So, if green chemistry green production processes can reduce the environmental impacts. So, not only about water it is also about energy it is also about persistent pollutants heavy metal pollution all these factors included. So, industries should should gradually evolve towards recycling their water 100 percent as much as possible. So, closed-loop production if that can be done then it will really you know that is the direction in which industry needs to evolve that will raise the costs of many products that we use. But again if the environment is bearing the cost presently if the cost is externalized the what do you mean by externalizing costs the price of the product does not include all the costs associated with that product. In other words if in manufacturing a product if somebody's water gets polluted somebody's land gets polluted that is a cost, but that is not included in the price of the product. So, it means that that cost has been externalized. So, we find many products which are cheap because costs have been externalized somebody else is bearing the cost for giving that product cheaply to you. So, sustainability requires environmental protection and even social justice. So, externalizing costs like that is not consistent with social justice why should somebody else bear the cost for the products that we enjoy. So, internalizing costs is a positive step yes some products will have will definitely become more expensive, but our economy also has to go through a learning process I do not think anything is perfect neither is our economy. So, what is the harm in evolving? So, we already saw about industrial symbiosis I showed you in the chapter on sustainable development. So, sometimes making closed loop systems within one industry may not be possible or it may not be very profitable for the industry, but if there is a network of industries which are sharing their resources then it probably would work out better. Now, there are some industrial waste which do not contain very harmful toxic or persistent chemicals and in those circumstances there are low energy alternative ways of treatment such as you have planted filters, you have constructed wetlands, IIT Bombay has also developed a very nice technique, DEWATS is another thing. So, I have given several resources there are cases of industries which have actually closed the water loop. So, what do I mean by closing the water loop that they operate in a closed loop they do not they do not there are no net input of water they use the water they recycle the water entirely. So, there in that reference you could you could go there and just maybe read up on the various companies mentioned over there. So, we looked at conservation in agriculture, conservation in industry and now coming to domestic water use and I have something very interesting to share with you over here a nice video again. Water use domestic water use is only 5 percent, but if that 5 percent of water which ultimately gets converted into sewage if that goes into a water body it can spoil very large amounts of water. So, even a small let us say a glass full of highly polluted water poured in a barrel of clean water makes that entire barrel of clean water unfit to drink. So, just because it is 5 percent it does not mean that it is any less important it should be treated well. And yes there are there are interesting ways of treating domestic water there are some issues, but even the conventional effluent treatment plants have some issues. So, there is no running away from issues. But one thing is that this is again one thing that I told you to keep in mind is that degraded soils can benefit from organic inputs of organic carbon and our sewage domestic sewage contains large quantities of organic matter. So, can we kind of tie both ends you know at one end the soils are lacking organic matter and at the other end the water is polluted because it has organic matter. So, why do not we tie the two ends? So, is it is it possible to use sewage water after some treatment for growing plants for instance. And it is possible there are there are places where people have irrigated using have they have it is not a good idea to grow food crops with sewage water or even reclaimed water because of fear of contamination by pathogens. But there is no harm in growing tree crops for timber or things like that. So, there is another issue of I told you about flushing with good clean water that is that is not the best idea. In fact, recycled water or reclaimed water if available can be used to flush, but you can as I said in the sustainability topic you need to think out of the box. Is it necessary to flush that is also something that you could ask and it turns out that many people have thought of it that way. There are composting toilets and in the video on Auroville that we saw there was a composting toilet that does not look very suitable for an urban lifestyle. But I have actually seen very comfortable and very nice looking composting toilets and they look very clean. So, they are western style toilet absolutely clean it does not smell at all and it is quite effective. So, there are composting toilets there are some available in India there are some brands which are very expensive, but I am sure we are very innovative lot and things can be made a lot cheaper. Now, there are alternative water treatment methods the conventional water treatment costs a lot of energy, but there are alternative methods and this is where I said you can click the hyperlink and watch videos. There are various methods that are listed over here they are really very interesting I request everybody to please in your notebook please note down this slide on alternative water treatment methods and go to each of those hyperlinks and check them out for yourself they are very interesting methods. I will just tell you what these constructed wetlands are you have some primary treatment may be settled down the solids and then you transfer the supernatant to a so, this is a horizontal flow kind of setup where you have some wetland plants that are planted in a in let us say like a trough of it is a tank which is like a trough and you have the water coming in and then the cleaned water going out. So, the microbial colonies that are associated around the roots of these plants they do the magic and you get reasonably clean water and you can you can obviously have serial arrangement or serial and parallel arrangement of such tank elements so, that you get water of the desired quality. So, there are again references and you can follow them there is one other method that I liked very much and I am just going to quickly explain to you this is what we normally do with our domestic sewage we have our domestic sewage we have an effluent treatment plant we pour in large quantities of electricity in it and we get reclaimed water but we also get some sludge and that sludge can pose a pollution problem it is it can be applied to land but then you know it can contain some pollutants. The problem is that this system although it yields reclaimed water it consumes large quantities of energy. So, there is I have cited the source over here this organization has developed a system where they have an open wetland with ducks and the domestic sewage comes into that open wetland and in the open wetland it is open to the sky. So, you have sunlight and when you have sunlight you have algae growing on it and then the ducks feed on that and as they feed they are paddling through the through the pond and because they are paddling through the pond it aerates the pond and more over with the beaks as they feed they are essentially they are atomizing the water because they want to get to the algae and they want to squeeze out all the water out of their beak. So, in the process it aerates the water. So, the the aeration costs are 0 the the flock of ducks is released they are put in a cage at night and in the morning they are released and they rush because they are hungry they rush to the to the pond and feed over it feed on it all all through the day come back to the cage and lay eggs. So, you get reclaimed water you get eggs all for for doing nothing just you just need to have those tanks and some the gentleman from this organization who had come to our institute he explained that a case study where the monthly electricity costs for that project were lakhs of rupees and they completely turned around the whole thing and it started yielding a few lakhs of rupees in profits by the selling of those eggs and getting the reclaimed water. Obviously, these these systems have got problems there are several problems one one problem would be what if there are persistent organic chemicals in the in the sewage. So, persistent organic chemicals are are not a good idea from a sustainability point of view anyway. So, they need to be eliminated if there are consumer products that are having such chemicals they need to be phased out these these products should not be on the market shelf if we want to talk about sustainability. It is not I mean it is a self-defeating approach you know to talk about sustainability and then allow such products to be on the shelf unless those things are done I mean none of the systems are going to work. I have just modified that and said that you can you could take some of the algae and you can that plant biomass can be converted into energy through either a biogas plant or a pyrolysis plant. So, you could you could add more and more elements, but it becomes a more complex system and then the infrastructure costs may be higher. So, you will have to strike a balance and that depends on the local conditions availability of things and. So, at at Amruta we have been working on similar systems and this shows how your solid waste the organic part of the solid waste the sewage and its treatment all can be integrated to yield multiple benefits. So, you can get treated water you can get vermicompost you can get biogas also and you can make some either food or fodder or wood as well as milk. So, you can get many outputs and you can tune which one you want more and which one you want less depending on the situation. We started some work we have a biogas plant and we are taking the effluent from the biogas plant treating it this is a constructed wetland it is an experimental setup for a constructed wetland and we take the effluent from the biogas plant and put it into this wetland and you have a three different treatments this is a simple sand filter and you have two units in series and this is a planted filter and this one has a different lower bed height. So, we are investigating I have a master's student from ETH Switzerland who is she is an exchange student who has come to Amruta to do her masters. So, this is part of her project and it is been going quite successfully we found a very significant BOD reduction as well as a significant reduction of ammonium, but rest of the results are not out yet. So, I would rather not comment on that. The last thing I have is a small video which is I showed you a success story and an environmental hero who did some work in villages, but you may say that we are not from villages and we live in cities. So, what can we do in cities? So, here is an example of what you can do in a city this gentleman in a busy city like Bangalore has used his roof to literally do wonders by recycling water. So, he again the same concept you know recycling water and producing food are not to be decoupled, but you can do all that in one system. So, he has done that and let us let us watch this nice video. So, we are almost at the end of this session. I have I have a list of things that we can do over here related to water there are several things that you as a person maybe as a family can do and I have listed down a few things over here, but I think your imagination is the limit and you could think of many more things to do and make some positive impacts on this issue. I think if you if you involve students in a constructive way, then this topic will become very very interesting for the students and I think it will give you also the satisfaction of having contributed in a in a significant way. So, I have I have some extra resources you could read upon. So, thank you very much have a good evening.