 Often a tank was constructed across a slope so to collect and store water by taking advantage of local mounds and depressions.Tank irrigation is practised by constructing mud banks across small streams to make a small reservoir which collect excess water during the rainy season.Tank use is especially critical in parts of South India without perennial rainfall where water supply replenishment is dependent on a cycle of dry seasons alternating with monsoon seasons.Water is considered a purifying and regenerative element in India, and is an essential element of prayer and ritual.