Fresh water is one of the world’s most precious and limited resources. Despite being incredibly valuable and difficult to replenish, it is exploited at alarming rates. A single family in the US, for example, can unknowingly waste as much as 180 gallons of water in a single week. Much of this can come from leaving the faucet on while washing dishes or brushing one’s teeth. As a result, a fair portion of the water waste remains relatively “clean”.
This “clean” wastewater, also referred to as grey water, comes from household plumbing systems like faucets, showers, washing machines, dishwashers, and garden hoses. It does not include water from toilets or any other sources that may be contaminated with significant concentrations of human waste or pathogens. As it does usually contain traces of organic waste and nutrients, it is not considered potable. Moreover, unless it is treated, it deteriorates over time and can produce an unfavorable odor.
In areas that experience droughts or water shortages, recycling grey water is a practical means of reducing demand for the central water supply. If you’re simply looking for a more cost-effective and environmentally-friendly way to lower your carbon footprint, look no further! It’s never too late to start collecting grey water and reusing it either indoors or outdoors, and the planet will thank you for it. Below are some of the most common forms and uses of grey water as well as some information on its safety and regulations.
Common Forms of Grey Water
In urban homes and buildings with various types of water systems, grey water is abundant. As a large number of people go about their day, they make use of considerable amounts of fresh water. Seasons with higher rainfall levels may also lead to the production of more “gently used” or “grey” water. To reuse this, it is necessary to install receptacles for its collection or to design pipe systems that can re-direct its flow to other parts of the home or landscape.
- Used water from the washing machine – if left untreated, this may not be applicable for use everywhere (especially in the garden) due to the presence of soaps or chlorine-based cleaners
- Used water from showers and bathroom sinks – may contain higher traces of human waste, but is much safer to use than blackwater (wastewater from toilets)
- Collected water from leaks in the ceiling or from loose taps
- Used water from the kitchen – usually contains the highest amounts of organic waste and nutrients; tends to require additional treatment prior to outdoor use due to the presence of grease and bacteria (from either cooked or raw food)
- Dirty water collected while cleaning surfaces – e.g. from a mop or rag
- Collected rainwater from storm gutters – usually the safest form of grey water for use in the landscape or for irrigation purposes in farms
Uses of Grey Water
1) As toilet flushing water
Residential toilets make use of about 1.6 gallons of water per flush. Depending on the number of people in a home or building, the wastewater produced by toilets can amount to about a third of the entire volume of water used annually. As there is no need to use fresh, drinking water to flush a toilet, grey water can be used to minimize toilet-related water waste.
In less developed areas that may experience water shortages, it’s fairly common to come across faucets that are paired with a pail (for water collection) instead of a fixed sink or basin. The water collected in the pail, either from washing one’s hands, bathing, or washing clothes, can then be used to “bucket flush” a toilet. Nifty inventions, such as Sink Positive, which incorporates a faucet and sink into the toilet tank’s lid, are particularly great for apartment buildings and other shared spaces.
2) As a source of moisture for ornamental or landscaping plants
One of the best ways to reuse your grey water is by redirecting its flow toward an ornamental garden or landscape. Gardens, greenhouses, and well-planted landscapes make use of large amounts of fresh water, especially outside the rainy season or during prolonged droughts. In fact, the amount of water used for outdoor plants can make up almost 50% of an entire household’s water usage. Of course, arid gardens with a larger surface area may easily account for more water than the amount used within a home.
Collected grey water (from a shower, sink, or washing machine) can be diverted toward a drain system that transports it to specific parts of the garden. The Laundry-to-Landscape and the Branched Drain system (both developed by Art Ludwig) are two efficient ways of using indoor-sourced grey water for outdoor locations.
As grey water contains organic waste and tons of micro-nutrients, it can aid in the growth of many outdoor plants. Some species, such as those which tend to favor alkaline conditions, are particularly benefitted by grey water. Plants that favor acidic and shady conditions are less likely to benefit from wastewater with soap residue. If you intend to use grey water for the majority of your garden, make sure to cultivate species that can tolerate salts and potentially strong alkalis.
3) For irrigation of farms and orchards
Many fruit-producing trees and shrubs thrive when their sprawling root systems are irrigated with grey water. Note, however, that while it can legally be used for ornamentals, there may be restrictions on its usage for many plants. In some states, there are laws against using grey water for food plants, with the exception of citrus trees and nut-producing species. Moreover, there are safety considerations and treatment requirements, especially in farms where grey water may come into contact with natural waterways.
4) For artificially constructed wetlands
Constructed, flow-through gardens that are planted with wetland species, like reeds, rushes, and cattails, are fantastic tools for stripping grey water of excess nutrients. These artificial wetland systems are usually composed of a settling tank for grey water and treatment cells with rows of wetland plants. These cells tend to be filled with sandy or rocky substrates through which water may easily flow (with the help of either gravitational force or pumps).
When maintained properly, a constructed wetland can be a visually appealing vertical or horizontal garden that meets many uses. As a tool for the phytoremediation of used water, it is eco-friendly and fairly straightforward to set up and maintain, even in rural areas. While it indirectly reduces pressure on drainage systems, it also helps protect nearby waterways from contaminants. That being said, this system is not advised in arid areas where the landscape is more likely to benefit from direct irrigation.
5) For washing tools or areas that don’t require disinfection
Grey water can be used to wash non-contact zones (i.e. surfaces that are not touched by bare hands or feet) like your own driveway, as long as the water doesn’t drain into other people’s properties, shared roads, or natural waterways. It should not be used in areas where the water may accumulate and become stagnant. Grey water can also be used to wash debris off of garden tools that you’re most likely to handle with gloves, like rakes and shovels.
Safety Concerns
Grey water may contain traces of human waste and disease-causing bacteria, especially if it is sourced from washers that have been used to clean soiled clothes. Handling it with bare hands is not recommended. Moreover, it should not be used as drinking water (even if it is passed through a filter), allowed to flow into storm gutters, or funneled into sprinkler systems for gardens. If you intend to divert its flow into your garden, aim to use a drip line that releases it into mulch or into subsurface sediments.
Before installing a greywater system in your home, think about the substances or organic materials that are most likely to accumulate in high concentrations. If your household makes use of harsh soaps, bleach, and other non-degradable chemicals, your grey water may not be suitable for use in outdoor environments. Keep in mind that, by using grey water to irrigate your garden, you may inadvertently introduce unnatural compounds into the wild.
Is It Necessary to Treat Grey Water Before Use?
The use of untreated vs treated grey water differs based on its source, its intended usage, and the jurisdiction where you reside. In some states, untreated grey water is tantamount to sewage water and cannot be legally re-used for surface irrigation. The regulations differ per state, with some adopting special policies for landscape irrigation, so it would be best to double-check with local government units prior to installing a grey water system.
Further treatment of grey water may be necessary as your source may introduce grease, toxic chemicals, strong acids, and other substances that may endanger outdoor plants and wildlife. When grey water is left unused and untreated for more than 24 hours, especially in warm climates, it often produces unpleasant odors due to the buildup of bacteria. In general, treated grey water is associated with fewer health risks.
Final Precautions on Grey Water Usage
While recycling grey water definitely has its socioeconomic merits and its positive impacts on the environment, it’s important to keep in mind that the best strategies for its use differ from case to case. Simply put, some types of grey water are safer to use than others. Some may be incredibly beneficial to the landscape, whereas the use of other types may endanger your plants or the members of your household. Below are some final precautions to remember prior to reusing your home’s grey water.
- Do not use non-natural soaps and harsh chemicals if you intend to reuse the grey water that comes from your shower, bathroom sink, or washing machine.
- Do not recycle water that has been used to bathe your pets or wash used diapers. This is more likely to carry high concentrations of bacteria and fecal matter.
- Do not use untreated grey water if it is sourced from the kitchen sink or dishwasher. This type of grey water usually requires additional treatment as it may contain pathogens from raw food, potentially harmful oils, and harsh dishwashing detergents.
- Do not hose, mist, or spray your garden with untreated grey water. Use a sub-surface irrigation system or a drip line. These methods of irrigation have lower health risks as they do not require direct handling and are less likely to aerosolize contaminants.
- Avoid using untreated grey water to irrigate your vegetable or herb gardens. It should only be used for ornamental plants, landscape plants, and other non-food plants.
- Do not store untreated grey water for more than 24 hours.
- Avoid exclusively using grey water for your garden. It would be prudent to alternate it with clean, fresh water as this should help dilute salts and re-balance pH levels.
- Do not reuse grey water that has come into contact with any parts of a toilet or bidet.
- Do not allow grey water to form stagnant pools or puddles in your garden. These may be sites of growth for vectors of diseases.
- Children or pets should not play in areas that are irrigated with grey water.
