What Is Greywater?

Updated October 23, 2026

If you live in the southern or central high plains and certain drought-prone areas, you'll know these regions often experience water shortages. These shortages lead to water restrictions and higher prices. However, a significant percentage of household water goes to waste as greywater. You can, with certain restrictions, reuse this greywater.

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What Are the Different Types of Wastewater in Plumbing?

Virtually all water, once used, becomes wastewater. There are different categories of wastewater, some of which you can reuse, while others require significant treatment.

• Domestic: This is water originating from homes and is the focus of this blog. It consists of grey water from showers, bathtubs, sinks, dishwashers and laundry, as well as blackwater from toilets.

• Industrial: Wastewater derived from industrial processes contains chemicals, solvents, heavy metals, acids and alkalis. It's not safe, and regulations require industries to pretreat industrial wastewater before discharge into municipal sewers.

• Agricultural: Water runoff from farms, crop fields and livestock areas contains fertilizers, animal waste, pesticides and sediment. If not carefully managed, agricultural wastewater can cause nutrient pollution in waterways.

• Stormwater: While seemingly clean, stormwater runoff contains pollutants, including trash, metals, salts and oils.

What Is Greywater?

The most common greywater definition is that it is domestic wastewater generated from the use of potable water in homes, and which does not contain fecal or E. coli contamination. The categorization of greywater depends on what is in greywater.

• Light greywater: This is lightly contaminated bath water, shower water and water from the bathroom sink and washing machine. It contains low levels of chemicals, soaps, fats, pathogens and suspended solids.

• Dark greywater: Water from kitchen sinks and dishwashers is known as dark greywater. It contains food particles, cooking oils, large amounts of suspended solids and sodium from phosphates in dishwashing detergents.

What Is a Greywater System?

Many authorities have regulations or guidelines on the use of greywater. These require homeowners to install a greywater system if they intend to reuse this water. Additionally, you should not store untreated greywater for longer than 24 hours to prevent the formation of odors and nutrient breakdown.

Untreated Residential Greywater Systems

You can use untreated light greywater for irrigation as long as the irrigation system is below ground and uses drip lines to feed the water into the soil. The best plants for greywater are fruit trees, shrubs, ornamentals and hardy vegetables like tomatoes, squash and corn. Avoid leafy greens and root vegetables, as soap residues may contaminate the plants and there's a risk of bacterial contamination. It's best to use light greywater. Untreated greywater plumbing systems include:

• Laundry to landscape: This is a simple, entry-level system that plumbs greywater from your washing machine discharge pump into subsurface mulch basins.

• Branched drain gravity system: If your land is sloped, you can use branched drains and gravity to direct water to multiple subsurface outlets.

• Pumped distribution system: Alternatively, use a pump fitted with a simple filter to distribute greywater to plants over a wider area.

Greywater Treatment Systems

While you can only use untreated greywater for subsurface forms of irrigation, if you treat the greywater, you may use it for other applications. Greywater treatment entails passing the water through a packaged greywater filter system that disinfects and treats the greywater to NSF/ANSI Standard 350. Many jurisdictions let you use disinfected greywater for flushing toilets and for standard drip irrigation.

How Much Does Greywater System Installation Cost?

According to HomeAdvisor, prices vary depending on the type of system you choose to install. You can expect to pay in the range of $2,200 and $5,000. This includes materials, labor and permits.

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FAQs

Is Greywater Safe to Drink?

While greywater is moderately safe, it's not suitable for drinking, and it's not safe for washing or cooking. Greywater quality also deteriorates over time. This is why you shouldn't store it for more than 24 hours.

What Is Greywater Used For?

Used correctly, greywater is safe and can reduce household water consumption. Light greywater contains virtually no pathogens, and it's unlikely you'll get ill from contact with it. Dark greywater contains food waste and chemicals, and the health risks are slightly greater, especially if you attempt to store dark greywater.

What Is Blackwater?

Blackwater is water contaminated by human waste and urine. It includes water from toilets and the water in a sewage system or septic tank system. Blackwater may contain high levels of bacteria, parasites and viruses. If greywater comes into contact with blackwater, it's immediately contaminated. You must keep greywater systems completely separated from contamination by blackwater. This especially applies to septic tanks, as well as septic tank overflows, spillages and backed-up toilets.

Is Blackwater Dangerous?

Blackwater is dangerous. It may cause diseases including gastrointestinal illness, liver disease and other illnesses, as well as skin infections from direct contact. When considering greywater vs. blackwater, you can reuse greywater, but you should never attempt to reuse blackwater.

How Much Greywater Does a House Produce?

Between 50% and 80% of household wastewater is greywater. The rest is dangerous, sewage-ridden blackwater. According to Oklahoma State University data, households produce about 78 gallons of greywater per day, on average.

Can Greywater Go Into a Septic System?

Considering greywater is the runoff from showers, washing dishes and doing laundry, a lot of it ends up in your septic system if your home has one. This is totally fine; your septic system was designed to handle it. If you choose to install a separate greywater system, the greywater is diverted before it reaches your septic system.