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. Graywater samples were collected from a washing machine with full load of laundry and a half cup of concentrated GAIN detergent.
She concluded that sodium and all other elements except boron were at concentrations low enough not to cause any injury to plants. The sodium adsorption ratio (SAR) values were well below the values of 15 that may cause soil dispersion from long term application of these graywaters.
Water pH values and their alkalinity values should not cause any problems. The measured pH of 6.4 and alkalinity of 40 compare favorably to the average levels in 216 well water samples from FY 07, which were pH 7.06 and an alkalinity of 56.2. The boron level in the first (soapy) wash might harm sensitive plants like peach, onion and barley….but you wouldn’t be using graywater on food plants anyway.
Bottom line, you can use graywater just like you’d use fresh water on landscape plants.
NOTE: 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.