Recovering household waste water for your plants and garden is often referred to as setting up a gray water system. In the U.S., recovering and rerouting water from your household runoff to the plants and garden is allowed in most communities, with some restrictions. Waste water recovered from washing machines, bathroom sinks and bathtubs or showers is generally allowed, while waste water from toilets is not. Water from the kitchen sink and dishwasher is allowed in some areas, but not allowed in others because it's considered a potential health hazard.
The amount of work required to set up a gray water system for your home depends on your home's design. For example, running the bathtub or shower drain to a backyard garden will take more work if the bathroom is located in the center of the house rather than next to an exterior wall.
Drill or saw a hole through the exterior wall of your home near the washer or sink that will be routed outside. Cut the hole just large enough to accommodate the size of your existing pipe or drainage hose.
Remove the washing machine drainage hose from it's current sewage pipe and feed it through the wall hole. For bathroom sinks, disconnect the drainage pipe underneath and connect a new pipe with couplings and bends as needed to reroute it through the exterior wall hole.
Attach outdoor pipes or hoses that extend far enough to carry the waste water to your chosen plants or garden.
Dig a small basin around the area where the water will discharge into the garden and fill it with 3 to 4 inches of mulch. This discharge area will act as a grease trap to collect hair, dead skin cells and other particle matter that will decompose over time.