CA's drought is wrecking havoc on farms and mature trees, but grey water can be used to reduce the impact on your yard. According to UCDavis, "Greywater is untreated waste water which has not come into contact with toilet waste." This includes water collected from the shower, bath, washing machine, or sink.
You should check with your local authorities to learn about specific restrictions on the use of grey water in your area. Grey water should never be considered potable (safe to drink). Personally, I avoid using it on food crops, but it does wonders on ornamentals, lawn, and flowers without wasting fresh drinking water.
You can grow a surprising amount of food in your own yard. Ask me how!