Groundwater Problems Caused by Irrigation with Sewage Effluent.

* As growing populations continue to increase competition for water, sewage effluent will increasingly be used for irrigation.

* Unfortunately, little or no attention has been paid to the long-term effects of sewage irrigation on underlying groundwater.

* In dry climates, most of the water applied for irrigation evaporates.

* Hence, concentrations of non-biodegradable chemicals in the drainage or deep-percolation water going down to the groundwater can be much higher than in the effluent itself (about five times higher for an irrigation efficiency of 80 percent).

* These chemicals comprise not only the salts, nitrates, and pesticide residues normally expected in irrigated agriculture, but also

-- "sewage chemicals" like synthetic organic compounds,

-- disinfection by-products,

-- pharmaceuticals and pharmaceutically active chemicals like endocrine disrupters, and

-- fulvic and humic acids.

* The acids form a new suite of disinfection by-products when the groundwater is pumped up again and chlorinated or otherwise disinfected for drinking.

* Thus, the groundwater below sewage-irrigated areas eventually may become unfit for drinking, which raises questions of liability.

* More research on long-term effects of sewage irrigation on groundwater is urgently needed.