Some elements in irrigation water may be directly toxic to crops. Establishing toxicity limits in water is complicated by reactions which take place once the water is applied to the soil. When an element is added to the soil from irrigation, it may be inactivated by chemical reactions or it may build up in the soil until it reaches a toxic level. An element at a given concentration in water may be immediately toxic to a crop because of foliar effects if sprinkler irrigation is used. If furrow irrigation is used, it may require a number of years for the element to accumulate to toxic levels, or it may be immobilized in the soil and never reach toxic levels.

At present the content of toxic elements in well water in Nebraska has not been found high enough to expect toxicity problems except for rare cases from boron. Excessive levels of boron are nearly always associated with deep ground water which also has a high salinity hazard. Irrigation waters containing more than 1.0 ppm boron (B) may cause accumulation of toxic levels for sensitive crops.