Residential greywater is all the wastewater from showers, bathtubs, bathroom sinks and clothes washers. It adds up to nearly 50% of the average household's water use. And while blackwater — wastewater from toilets and the kitchen sink — is complicated to process for reuse, greywater is commonly recycled for landscape irrigation and even for filling toilets in the home. Products for processing and delivering greywater vary from simple watering systems to multistage treatment and storage appliances.
Types of greywater systems
Treatment of greywater covers three basic levels: untreated (raw), filtered and treated. The level of treatment determines the appropriate uses of the greywater. In general, untreated water typically is limited to subsurface irrigation of ornamental plants. Filtered water can be used for watering plants above ground, which may or may not include edible plants. Treated water is often used for a variety of landscape applications, including sprinkler systems, as well as for flush water in toilets.
In addition to legitimate, built-in systems, you can find a number of greywater devices, such as small-scale capture systems that might be little more than a sink-top drain basin leading to a bucket. However, these devices have very limited capacity, and pouring untreated greywater onto the ground can introduce a range of contaminants that can be hazardous on edible plants and ultimately can pollute natural water systems. For the same reason, it's not a good idea to attach a garden hose to the discharge pipe on your washing machine and run it out to the yard.
All types of processed greywater cannot be stored for extended periods, so systems must be designed to use the water immediately or to automatically empty the holding tank after a timed period of inactivity.
Simple systems for raw greywater
A basic greywater recycling kit can be as simple as a specially designed barrel that collects the water from the home's fixtures and allows gravity to deliver the water to planted areas via underground PVC pipes. Solid debris, such as hair and dirt, are filtered out with filter screens and/or they are separated naturally inside the barrel, much like in a septic tank. Smaller versions of this kind of system may serve only one fixture, typically a clothes washer.
Systems for filtered greywater
Be aware that while filtered greywater is a step up from untreated greywater in terms of purification, it's not treated to remove all pathogens and organic compounds, including human waste. Systems that filter greywater typically include a holding tank, pumps and a number of filtering devices. Basic setups may have only a sand-type filter, while more sophisticated systems feature multistage filtration. Most filtered greywater systems are used to irrigate gardens and landscapes through subsurface piping or aboveground drip irrigation.
At present, the most you can do with treated greywater indoors is use it to fill your toilet tank. There are advanced treatment systems that make greywater potable (drinkable), but reusing greywater for anything but toilets is prohibited in the United States. Treated greywater is first filtered to remove debris, then it's treated with a chemical disinfectant before passing through UV light for additional purification. Systems range from sink-to-toilet units that fit in a bathroom vanity to whole-house appliances that go in a utility closet or basement. Treatment systems have their own dedicated plumbing lines, including vents, and distribute treated water to toilets and landscape systems via electric pumps.
There's a good chance that treatment, storage and use of greywater are strictly governed in your area. So before you do any shopping for a greywater system, check with your city office or building department. Don't assume that any product or system is approved for your area, regardless of the manufacturer's claims or if the same system is used widely elsewhere. Also be sure to ask about permits, which are required in most areas for installing a greywater system.