When you visit Laura Allen’s garden in Oakland, it’s hard to believe that when she moved there in 2003 the yard was completely covered in concrete and weeds. She transformed the neglected space into a bountiful garden that produces bumper crops of fruits, nuts and vegetables without using a lot of potable water.

Allen is one of the founders of Greywater Action, a grassroots group that empowers people to “build sustainable water culture and infrastructure,” and uses her home garden to experiment with different greywater technology. According to Greywater Action, greywater may contain traces of dirt, food, grease, hair, and household cleaning products, and while it may look dirty, it is a safe and even beneficial source of irrigation water for a garden. If released into rivers, lakes, or estuaries, the nutrients in greywater become pollutants, but when released in a garden they become valuable fertilizer.

Allen recommends “simple, low-tech greywater systems that use gravity whenever possible, instead of pumps,” and she prefers irrigation systems that are designed to avoid clogging, rather than relying on filters and drip irrigation. Her home greywater system drains directly to her garden and waters several fruit trees, ornamental plants, and an in ground wetland (papyrus, taro, irises). She makes sure to only use all-natural, biodegradable soaps that will not harm her plants.