Use your washing machine gray water to water the garden or lawn. Marsha Duttle of New Mexico State University's College of Agriculture reported in 2007 that all gray water (not just that from washing machines) can be used to water plants safely. There are several caveats, however. You must use only the gray water from the prewash or rinse cycles, since the water from the wash cycle may have chemicals in it from your detergent or other cleaning agent (e.g., borax). Don't put it on root crops (e.g., carrots) that you plan to eat raw, and apply the water directly to the soil rather than sprinkling it on top of the plants. Don't use it on plants that are just getting started, and be careful not to use it on plants that like a little more acidity in the soil, since the water will have a higher pH level.
Have the gray water from your washing machine pumped into your toilet tank. Both toilet water and washing machine gray water go to the septic tank anyway, so rerouting the washing machine gray water is only asking it to do one more job on its way out of your home. This is one of the biggest ways to conserve water in your home; Duttle claimed that up to 50 percent of water usage in the home can be attributed to toilet flushing.
Use the gray water for tasks that will result in dirty water anyway. Examples include washing the car, rinsing paint brushes, or scrubbing out an oil stain from your driveway, steps, or sidewalk.
If you plan to use washing machine gray water that isn't treated, use it right away. Storing it for more than a day makes the growth of bacteria much more likely. To reduce the amount of chemicals in the water, avoid adding liquid fabric softeners to the wash, and use dryer fabric softener sheets instead.