As many regions’ water costs rise, more people are asking if the water that flows down their drains after bathing and washing—known as graywater—can be used to water gardens. Increasingly, state permitting authorities are saying yes—with conditions.
In Arizona and New Mexico, homeowners can drain graywater right onto their lawns and landscapes. In states where laws are more stringent, especially California, underground graywater irrigation systems—some involving sophisticated water sensors that direct water to where it’s most needed—are popping up. You can help the earth and reduce bills by installing a system yourself. Though regulations vary by location, setting up a fairly simple water-reuse system in your home is becoming easier and more common.
A graywater overview
Preparing graywater requires a few basic steps: draining it from the house to your graywater system via pipes kept separate from toilet drains; filtering out fibers and greases; then disinfecting the water and treating its carbon. You can take care of the last two parts—disinfecting and treating carbon—by setting up a system in which graywater drains under a few inches of soil, gravel and plant roots. The plants and soil will naturally treat the carbon and disinfect the water.
Though kept separate from what’s flushed down the toilet—called «blackwater»—graywater still can contain bacteria and pathogens that could cause illness, although the small amounts present in most graywater are a low risk, according to a University of Massachusetts study. Graywater also contains carbon from oils, soaps and skin. As in all organic compounds, that carbon will decompose, potentially causing odors and clogging the air spaces in the ground. Health officials advise draining graywater under three to 18 inches of soil, where soil bacteria decompose carbon and destroy pathogens—and where plant roots can drink it up.
State regulations for graywater vary widely, so check with your municipality to be sure your system is legal. Some states consider kitchen-sink and dishwasher drainage blackwater because it contains grease, nutrients and food bits.In most states, graywater cannot be used above ground without a special permit. In nearly all states, a graywater permit requires submitting results of a soils test and an approved plan.
Laws are changing fast throughout the country; if your state or town doesn’t address graywater, help pave the way by applying for a special permit.
If you’re renovating a bathroom or building a house, consider installing graywater drainage pipes—even if you can’t or don’t plan to use graywater now. In the future, water recycling will likely become the norm as this resource gets too precious to throw away!
Although plants can disinfect graywater, pouring carbon-laden graywater directly onto your lawn can cause odors and clog drip-irrigation emitters. Avoid this by keeping graywater oxygenated so fast-acting aerobic bacteria can consume carbon and pathogens. Specialists recommend three ways to treat graywater’s carbon: (1) add an air diffuser to your surge tank, (2) design systems that cascade water, or (3) simply apply graywater only to gravel, course sand or well-aerated mulch, all of which have lots of air spaces for aerobic bacteria to work.
A typical graywater system includes:
- A surge tank to which all graywater first drains. This tanks equalizes and cools graywater flow so it doesn’t inundate the system with a deluge of hot water. A septic tank or 55-gallon drum, this also serves as a grease trap if the scum is periodically skimmed.
- A filter to remove clogging particles such as hair. You can buy a filter (see «Resources,» below) or make one with a nylon stocking. For grease and sludge, use a grease trap—essentially a box with a baffle that holds back scum so it can be skimmed out.
- Porous substrate, fluffy mulch or aerated tanks to promote fast-acting aerobic biological decomposition.
- Irrigation components such as perforated pipe and drip-irrigation lines that get graywater to the plants.
- Thirsty plants to use up nutrients and provide root systems that support microbes, which decompose carbon and germs in graywater.
- A diverter valve, which is essentially a switch that lets you divert graywater to the sewer or septic system if your system is overloaded or if chemicals such as toxic cleansers have been drained. –NH
How to Make the Health Inspector Happy
When applying for a permit, you might encounter a skeptical water authority or health agent who grants permits for wastewater systems. Your chances of success are higher if you:
- present an underground (called «subsurface») system
- use a diverter valve to assure you can switch graywater flow to a septic system or sewer
- prove your soil will absorb water
- show that your system is sufficiently distanced from groundwater and shores
The State of Regulations
In all states but Arizona and New Mexico, you’ll need a graywater-system permit to install a legal system. (Some exceptions are made in very rural areas.) Few states specifically address graywater systems beyond requiring a full- or reduced-size leachfield, often with a full-size septic tank. A septic tank can be replaced with filters; if your permitting agent balks at this, apply for a variance to do it. (Most permitting authorities won’t allow graywater on root crops.)
- California pre-approves two systems: a reduced-size shallow leachfield and a drip-irrigation system. Local permitting authorities know these systems are allowed if soil conditions and other factors are right. Homeowners must get tests to show their soil absorbs water and that groundwater isn’t nearby
- New Mexico adopted a graduated standard that allows surface irrigation with up to 250 gallons of graywater per day without a permit, with overflow to a septic system or sewer. Water used for washing anything soiled with excrement is categorized as blackwater (sewage).
- Arizona’s Type 1 Reclaimed Water General Permit lets private residences irrigate with less than 400 gallons of untreated graywater per day if it’s discharged at least 5 feet above the groundwater table. The law calls for filtration but does not specify the means.
- Colorado’s complex water-rights laws sometimes require home-owners to appeal to Water Court to use graywater and rainwater.
- Massachusetts allows graywater to be dispersed under 9 inches of soil and to be pretreated via a septic tank or a graywater filter approved by the state’s plumbing board.
- Washington, Minnesota and other states provide graywater-use permits, which usually require discharging graywater below ground.