 In a context of growing water scarcity, water accounting is a critical approach to set the information basis to achieve safe and sustainable water use. Effective water accounting allows water resource managers and farmers to determine the impacts of their strategies and practices and track the effects of changes. To summarize, the ability to effectively account for water use is essential in helping water authorities and farmers drive improvement and become aligned with external stakeholders' expectations as well as their own efforts to advance sustainable water management, especially underwater scarcity scenarios. We talk about water accounting and we ask ourselves why that is important and we ask ourselves that question at many different scales. At the basin scale, at the irrigation district scale, at the farm scale and we are not always aware of the importance of knowing the water that we use, we consume and we return to the system, to the hydrological system. We are not aware of the importance at each level, so each responsible of water management at a given scale has the need of knowing the water that is used for different reasons. One, because it costs money, pumping, transporting water is costly. Second, because we deal with water resource that is limited. And third, because by not doing a good use of water we can damage the environment where the irrigation activity takes place. So now we have to understand in the water accounting process the principle of the water balance. In the water balance we distinguish different components. We have our resource, the water that we are applying to the field and now we are going to focus on the field scale. Once it is in the field that water is stored for a given time in the soil to be consumed by the plant, but not all the water that is applied is consumed by the plant. Part of that water is lost through the evapotranspiration process or it can return back to the hydrological system by deep percolation or surface drainage. So how can we evaluate these different components? Some of them are easy or relatively easy to measure. Others can be estimated with good accuracy. Others are really difficult to measure or estimate, so we make use of the water balance to compute our accounting. And we obtain those components as the residual of the water balance. That's why the water balance equation is so important. Everybody has heard about different methods of estimating evapotranspiration. We are aware about the damage that we can cause with drainage water and deep percolation of water. If it is loaded with agrochemicals, that's very difficult to evaluate. And what we do can do is to measure the applied water. And for that we have to consider how the water gets to the field and the irrigation method that we are using. In general it's easier to measure the applied water if it comes through a pressurized pipe. Then we have very standard methods based on a propeller, current meter or ultrasonic principles or the magnetic flow meters that can be installed at the pipe in the proper position. And we can obtain the flow rate or the cumulative applied water. That's not difficult anymore and it is being implemented in most modernized irrigation districts in many Mediterranean countries. Maybe the difficulty comes when we apply the water using surface methods. Again, that is more complicated but the principles come from the old days when the hydraulics were developed and now we can combine the classic hydraulics with water level sensors that can be used in a continuous way, recording those water levels and give us for those flumes or wheels that are installed in the open channels measurements of flow rate but also the water that has gone through that device in a given time. So there is no excuse for not measuring the applied water even when we have open channels. Although we have to recognize that that is more difficult. As we've seen there are several options at different scales to account for water. Given its relevance, more effort should be made by the different stakeholders to establish a proper water accounting system adapted to the local conditions that allow making informed decisions under water scarcity situations.