Competition for water in California between rapidly expanding industrial-urban activities and agriculture undoubtedly will lead to usage of waters of varying quality. Although standard criteria for water quality are at hand, they do not usually include a consideration of lithium—which may pose a hazard to certain plants. Lithium content may vary widely. For example, a previous report established the presence of lithium in a number of well-water sources, varying in concentrations from 0.05 ppm to 0.50 ppm lithium. Lithium injury in some citrus orchards had been associated with irrigation waters containing concentrations of 0.10 ppm lithium or higher. With information on lithium hazard to economic plants limited thus far to a few citrus orchards, diagnostic criteria are needed, and the effects of lithium on other crops should be studied.