Poor irrigation management: a threat to soil, water and food security Poorly managed irrigation contributes to water shortages and pollution, land degradation and the spread of waterborne diseases. In many regions, water is being pumped out of the ground for irrigation faster than it can be replenished. Overpumping in India's Tamil Nadu state has lowered the water table by 25 to 30 m in a decade. XXX     pdf version of this graph XX Much of this water is wasted. As much as 60 percent of the water withdrawn for irrigation often does not reach the crop. It is lost through canal leakage, spillage, infiltration and unproductive evaporation, although some of this water reaches the river or groundwater, allowing it to be used by others downstream. Poor drainage and irrigation practices lead to waterlogging and salinization, which have sapped the productivity of nearly 50 percent of the world's irrigated lands. Unless irrigated fields are drained properly, salt builds up in the soil as water evaporates, making the land infertile. Salinity now affects more than 20 percent of the irrigated land in China and Pakistan.