Demand for electricity is highest during winter time. The water reservoirs need to be full then. This means that water is stored during summer, while demands for irrigation water are highest. Political setting Demands and availability of water in the five states are different and change over time. As water is scarce, this generates political friction, which is fed by other issues like territorial disputes.
All water contains a little salt.
Irrigated land will evaporate part of the water, leaving behind the salt. This salt will accumulate over the years, unless washed away, which requires a lot of water.