Irrigation already accounts for about two thirds of water use worldwide. As rivers and lakes are dammed, dried up, or polluted, and as food demand grows in the next 50 years, farmers will become increasingly dependent on groundwater for irrigation. Groundwater also plays a key ecological role by replenishing rivers, streams, and wetlands. One third of the wells tested in California's San Joaquin Valley in 1988 contained the pesticide DBCP at levels 10 times higher than the maximum allowed for drinking water-more than a decade after its use was banned. In the northern Chinese provinces of Beijing, Tianjin, Hebei, and Shandong, nitrate concentrations in groundwater exceeded the health guideline in more than half of the locations studied in 1995.
Water recycles extremely slowly underground, too slowly to flush out or dilute toxic chemicals.
Water that enters an aquifer remains there for an average of 1,400 years, compared to only 16 days for rivers. Thus Londoners, for example, may be drinking water that fell as rain as long ago as the last Ice Age. The urgency of preventing groundwater contamination is highlighted by the costs of cleanup efforts. To preserve this valuable resource, we need to make systematic changes in the way we grow our food, manufacture goods, and dispose of waste. The report proposes retooling industrial agriculture to reduce farm runoff, a leading source of groundwater pollution.