According to EPA estimates, nearly 50% of the clean, potable water delivered for use inside an average home in the U.S. goes down the drain from sinks, showers, and washing machines. So finding a way to put this “lightly used” household wastewater—otherwise known as greywater—to work flushing toilets and irrigating landscaping could cut a home’s consumption in half.

Plumbers in Europe, Canada, Japan, and Australia are already as familiar with installing greywater systems as they are bathtubs and kitchen sinks. But here in the United States, the adoption of on-site water recycling has only just gotten started. And as more cities and states explore and open up to greywater systems, the technology and the technicians to install it are becoming more available and affordable. Still, we’re a long way from common practice.

SHADES OF GREY

In broad strokes, greywater recycling systems come in three categories of complexity and cost: Untreated greywater used for deep-water (i.e., root-level) ornamental landscaping; filtered greywater to water landscape including vegetable gardens; and treated greywater for most non-potable uses such as flushing toilets.

Untreated Greywater Systems. The simplest and least expensive systems separate and drain greywater from sources such as the washing machine and shower, and then, using gravity, pipe this raw greywater to deep-water ornamental shrubs and trees. In some municipalities, such as San Francisco, a homeowner can install a small, simple greywater system (single-fixture and/or clothes-washer systems) without a permit. Many homeowners concerned with water consumption simply discharge washing machine or shower drains straight into garden troughs, but there exist legitimate public health concerns with surface application of raw greywater, especially on edible plants. For one, greywater can still contain organic compounds, such as fecal matter from soiled clothing, diapers, or bathing. Greywater can also contain high levels of phosphorus, good for the garden, but not rivers and lakes.

Therefore, most jurisdictions that permit the recycling of untreated greywater require it piped and disposed of below the frost line to deep-water ornamental trees and shrubs. All jurisdictions prohibit the storage of raw greywater; after 24 to 48 hours of fermentation it becomes septic blackwater. This lack of storage limits the practical application of untreated greywater as production and consumption do not always match. But a raw greywater system can cost under $300 in materials to plumb, so consequently many thousands of simple washing-machine-to-watering-can systems exist, some legal, most not.

Filtered Greywater. At once practical and moderate in cost ($1,500 to $3,000), a filtered greywater system represents the most popular option. Filtered systems can use pumps to distribute water through drip irrigation for watering ornamental and, in some areas, edible plants. No jurisdiction allows the use of filtered but untreated greywater indoors, nor the aerial spraying of greywater, such as lawn sprinklers.

At the low end, filtering methods include a simple skimmer, similar to that used for a pool, and a fine sand filter. More sophisticated systems employ multi-stage coarse-to-fine media (screen) filters, and even biological filters that incorporate contaminate-scrubbing vegetation. The simpler systems are generally used for deep root watering, or sometimes gravity-fed irrigation. The removal of fine particles in the multi-stage filtered systems allows the filtered greywater to run through pumps and drip irrigation without clogging.

Although legal for drip-system irrigation in some areas, the filters do not remove fecal matter, so users should be aware of the risk when watering edible plants, such as lettuce, which could transmit disease. The filters need periodic cleaning, and the frequency and intensity of maintenance required should figure prominently when considering a system; if the homeowner cannot maintain it properly, it will not work.

Treated Greywater. In order to store and recycle greywater for use in toilets, the greywater has to be filtered and treated. Many different treatment methods exist, and prices range from a few hundred dollars for a small, single-fixture point-of-use application, such Sloan’s Aqus System, to pricey, multi-stage in-home treatment plants that cost $8,000 or more and can feed multiple fixtures, such as the German AquaCycle system by Pontos.

Greywater treatment methods vary, but usually consist of a two-stage, coarse-to-fine filter that removes particles, followed by a chemical disinfectant (think chlorine tablets) or a biological (aerobic) treatment, and pass through ultraviolet light. The treated water is stored in a gas-tight container and pump-fed to toilet tanks to be used on demand. If there is not sufficient greywater stored, most systems have automatic valves with backflow preventers to make up the shortfall with fresh water. When there’s too much greywater, most systems have overflow valves that allow the excess to discharge into the sewage system.

Although some systems clean water to potable levels, no jurisdiction in the United States allows the use of site-treated water for anything other than toilets. Public treatment plants are monitored by the EPA; there’s no way to know if homeowners run their home-based treatment plants to the standards of a municipal sewer.