Q: I’ve been using gray water from my washing machine on landscape plants. In my research I found that my plants prefer acid soil and that gray water has a higher pH. Can I add something to the graywater to lower the pH?
A: Dr. Leticia Sonon, Program Coordinator at the UGA Soil Lab, recently analyzed the water collected from a washing machine with a full load of laundry and a half cup of concentrated GAIN detergent.
She concluded that laundry water pH values and their alkalinity level should not cause any problems in the landscape. The graywater pH of 6.4 and alkalinity of 40 compared favorably to the average levels in Georgia well water samples, which were pH 7.06 with an alkalinity of 56.2. Dr. Sonon found that sodium and all other elements except boron were at concentrations low enough not to cause any injury to plants. The boron level in the first (soapy) wash might harm sensitive plants if you pour the water in a single spot regularly. Other detergents might not have the same chemical content but this is the best information I have at this point.
(Editor note: Please make this a separate paragraph to end my answer above)
Graywater should NEVER be used in a vegetable garden. The possibility of disease transmission and food contamination is too great. Most water providers exempt food gardens from current water rules, so tap water can be used when irrigation is needed.