Guide M-106
Revised by Marsha Duttle, Extension Research AssistantCollege of Agriculture, Consumer and Environmental Sciences at New Mexico State University (PDF for printing)
Gray water is water used for dishwashing, laundry or bathing. In principle, all water discharged from a household, with the exception of toilet waste, is gray water. While this used water can contain grease, food particles, hair and many other contaminants, it can still be reused. Gray water reuse serves two purposes: it reduces the amount of fresh water needed to power the household and reduces the amount of wastewater going to the sewer or septic tank.
The New Mexico Department of Environmental Protection and the Department of Construction Industry manage New Mexico's liquid waste disposal and licensed systems. The use of gray water is restricted by the Liquid Waste Disposal Regulations (LWDR), however the Department of the Environment may grant an exemption if the applicant can demonstrate that:
“Granting an exemption will protect public health and the environment at a level at least equal to the minimum level of protection provided by the differentiated requirement” (LWDR, Section 202.D.2.); AND
"The proposed sanitation system, alone or in combination with other sanitation systems, will not pose a risk to public health or cause any degradation of any body of water" (LWDR Section 202.D.1).
GREYWATER APPLICATIONS
The amount and quality of greywater will determine in part how it can be reused. Irrigation and toilet flushing are two common uses, but almost any touchless use is possible.
Gray water is suitable for watering lawns, trees, ornamental plants and food crops. While greenhouse watering methods can be very different from outdoor watering, some tips for using gray water apply to both situations.
Apply gray water directly to the soil, not with a sprinkler system or any other method that would allow contact with the above-ground portion of the plants.
Root crops that are consumed raw should not be irrigated with gray water.
Plants that only grow in acidic soil should not be watered with alkaline greywater.
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Spread gray water widely and swirl fresh water around to avoid sodium salt buildup.
Even when irrigating outdoors, gray water should only be used in shallow areas where runoff is unlikely. A cloth bag attached to the end of the hose helps distribute the water and also serves as an additional filter. The filter should be removed and cleaned regularly (every three to four days).
In arid areas where dry grass or undergrowth pose a fire hazard, homeowners may want to create a firebreak or "green belt" of select high-humidity species. Gray water is ideal for firebreak irrigation because it adds plant nutrients to the process.
Keep in mind that in most areas, external irrigation is a seasonal use of greywater, but greywater is produced year-round. If it is not possible to return to the sewers or septic tanks in winter, look for applications that are suitable for all seasons.
Flushing toilets can use significant amounts of gray water, typically accounting for up to 50% of indoor water use. Poor quality gray water is not a problem when used to flush toilets as the water ends up in the sewer or septic tank where it would end up if not reused. Gray sewage should be pumped into the toilet bowl for flushing.DO NOTPour gray water into the toilet tank. Not only can gray water in the tank cause the flushing mechanism to fail, it can also cause a back pressure in the fresh water supply if the water pressure suddenly drops.
Algae can grow in lagoons or ponds with gray water, feeding fish in a separate pond or providing food for ducks and other waterfowl. Removing the algae is necessary to keep oxygen in the system and prevent odors. Ponds are often lined with concrete, stone, or plastic to prevent leaks. This method is a relatively inexpensive and easy way to recycle water, but it does require some knowledge of finding and building lagoons.
In an automatic washing machine, the wash water from a lightly soiled load or the rinse water can be saved for the next load. If you reuse laundry water for irrigation, do not use fabric softener or detergents that contain fabric softener (use fabric softener sheets in the dryer instead). Do not reuse water if the wash contains diapers. Wash water containing gasoline, diesel or similar contaminants should not be used for any purpose other than rinsing.
Untreated gray water
Untreated gray water should not be stored for more than a day, but adding two tablespoons of chlorine bleach per gallon of water will slightly increase storage life. Try to use gray water on the day you take it, otherwise the high bacteria count will cause unpleasant odors.
When using untreated greywater, observe the following precautions:
Gray water that contains sodium, bleach, or borax can harm plants. For this reason, water from automatic dishwashers should not be used for watering.
Water used to rinse kitchen utensils in the sink may contain fats, grease and oils and is not suitable for gray water use.
If you want to use washing machine water, avoid fabric softeners and detergents with fabric softener. Use the dryer fabric softener sheet instead.
GRAY WATER TREATMENT
Investing time and equipment in a system to filter, store, and possibly sanitize gray water can make water reuse a more convenient practice. Here are some questions to answer before building a treatment system:
How much gray water needs to be treated? About 65% of domestic wastewater is gray water. Bathing and washing can produce significant amounts of gray water in a large household.
What impurities are there? Gray water from the bathroom has different properties than that from the kitchen (see Figure 1).
What are the possible uses after the procedure? Planned greywater applications may require more or less treatment. Some uses, such as outdoor irrigation, are seasonal. Gray water is produced all year round.
What type of soil and groundwater level is there at your location? The shallow water table that lies beneath the sandy soil may be at risk of becoming contaminated.
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The answers to these questions will help you decide what type and size of system to install. Because greywater treatment systems are not in high demand, you may need to design and build a system to suit your own specifications and needs. Options to consider for gray water treatment include clarifiers, sanitizers, and filters.
Figure 1. Qualitative properties of selected domestic wastewater.(The drawing has been modified from the original version to be programmable in HTML format. Please view the PDF file or contact NMSU Agricultural Communications for the original hard copy.) __________________________________________________________________________Water Source Characteristics____________________________________________________________________________ Automatic Laundry Dishwasher, Bleach, Scum, High pH, Hot Water, Nitrates, Oil & Grease, Oxygen Demand, Phosphate, Salinity, Soaps, Sodium, Slurries & Turbidity, Automatic Dishwasher Bacteria, Scum, Food Particles, High pH, Hot water, fragrances, oils and fats, organic matter, oxygen demand, salinity, soaps, suspensions and turbidity, bath and shower bacteria, hair, hot water, fragrances, oils and fats, oxygen demand, soaps, suspended solids and turbidity, evaporants Cooler salinity Kitchen sinks, including kitchen bacteria, food particles, hot water, odor, oil and grease, organic matter, oxygen demand, soaps, suspended solids and cloudiness Chlorine and pool salinity
Panzer
In a settling tank, solids and large particles settle to the bottom while fats, oils, and small particles float to the top. The remaining liquid is reused. The sedimentation tank also allows the hot water to be cooled before reuse. The tank should be large enough to hold twice the expected flow plus 40 percent to allow for sludge accumulation and peak loads. One of the types of settling tanks that work well for gray wastewater treatment is the septic tank. A septic tank is specially designed for sedimentation. However, using a septic tank to treat gray water should not be confused with the traditional use of a septic tank. Gray waste water intended for reuse should NEVER be mixed with toilet waste.
Gray water flowing from a septic tank contains little or no oxygen. Gray water from an oxygen tank contains more oxygen, which is better for irrigation purposes. An electric pump or aerator added to a septic tank can create an oxygen environment. Aerobic conditions allow some decomposition of the waste in the tank and can help minimize sludge build-up and clogging in the system. Both oxygen tanks and septic tanks need to be pumped out every three to five years.
Various types of tanks may be suitable for settling or storing greywater. In addition to the commonly used metal, polyethylene, fiberglass, or wood tanks, consider using plastic trash cans, 55-gallon dims, portable pools, or waterbed mattresses.
disinfection
The two chemicals used to disinfect water are chlorine and iodine, with chlorine being the most common. Not only is it readily available (as liquid household bleach or in pool shops) and relatively inexpensive, it is also shelf stable and will evaporate from the water over time after disinfection. Organic matter in gray water can combine with chlorine and reduce the amount available for disinfection. For this reason it can make sense to install a filter or settling tank in front of the disinfection point.
The organic material is less affected by iodine, lasts longer and may be more effective in high pH greywater. Iodine is also fast acting, taking no more than two minutes to kill most pathogens.
There are several devices on the market that deliver appropriate amounts of iodine or chlorine (in solid or liquid form) into the water system. Contact pool suppliers or water treatment companies.
Filter
The type of filter required for a gray water system depends largely on the amount of gray water to be filtered and the type of contaminants present. The drain filter is a simple and inexpensive way to filter lint and hair from bath or laundry water. For outdoor watering or similar applications, a simple cloth bag attached to the end of a hose or pipe may suffice.
There are many types of commercially available water filters. Most use a charcoal, cellulose, or ceramic cartridge that needs to be cleaned or replaced periodically. Before purchasing a filter, determine whether it is a gravity filter (for small volumes) or a pressure filter (for flow rates over 20 gallons per minute). Also consider frequency, cost and maintainability.
Slow sand or media filters are usually built by the homeowner. These gravity filters can be constructed in a 55 gallon drum or similar sized container. Items that should be part of the filter include a perforated plate or other device to evenly distribute the water at the top, a concrete funnel at the bottom to allow the water to drain into the perforated drain pipe, and a cover and vent to prevent odors. Fill the bottom of the filter with rocks that are too big to get down the drain pipe.
Slow sand filters are shallow layers of stone, medium gravel, and pea gravel beneath a deep layer of sand (see Figure 2). A slow sand filter processes about 0.05 to 0.13 gallons per minute per square foot of surface.
The media filters are filled with various media such as fine sand, coarse sand, gravel, stone and wood shavings in order of increasing size to a total depth of 2 1/2 to 3 feet (see Figure 3).
NOTE: Figures 2 and 3 are not available. Please view the PDF or contact NMSU Agricultural Communications for a hard copy.
Slow sand filters require regular cleaning and replacement of the top layer of media. Media filters require less cleaning, but all layers must be cleaned or replaced when maintenance is required. If the gray water is passed through the settling tank before filtering, contamination is reduced and the intervals between cleaning can be extended.
Figure 4. Treatment of water quality variables(Figure 4 has been modified from the original version to be programmable in HTML format. See the PDF for the original printout or contact NMSU Agricultural Communications for the original printout.)
____________________________________________________________________________________________Treatment Variables__________________________________________________________________________ Odor, Organics, Oxygen Demand, and pH Alum Soaps and Haze Carbon Filtration Odor Chlorination Bacteria and Odor Plant Filtration Bacteria, Food Particulates, Suspended Solids, and Haze Plant Uptake Nitrates, Phosphates, Soaps, and Sodium Dilution Hot Water, Nitrates, pH, Phosphate, Salt and sodium filtration. Food Particulate, Oil & Grease, Organics, Soaps, Suspended & Haze, Flotation Oils & Greases, Hydrogen Peroxide Bacteria & Odor, Limescale Bacteria, Odor & Sodium Deposition Scum, Food Particulate, Hot Water, Organics, Oxygen Demand & Suspended Solid Bottom Filtration Bacteria, Bleach, Chlorine, Scum , Food Particulates, Organics Oxygen Demand, Particulate Matter and Turbidity Soil Uptake Nitrates, phosphates, soaps and sodium storage foam, Food Particulates, Hot Water, Organics, Oxygen Demand, pH and Suspended Solids
(Figures 1 and 4 reprinted fromwater and wastewater engineering(z. B. Scranton-Gillette Communications, Inc.)
New Mexico State University is an equal opportunity and affirmative action employer and educator. Cooperation between NMSU and the US Department of Agriculture.
Written January 1990Last modified: February 1994
Posted on the server: April 4, 1996
FAQs
How safe is the use of greywater? ›
When handled properly, greywater can be safely reused for the garden. Never re-use water from toilets, washing nappies or kitchen water. Do not use greywater on vegetables, fruit, herbs or anything you plan to eat.
Can you use grey water to flush toilets? ›Poor quality greywater is not a problem if it is used to flush toilets, because the water goes into the sewer or septic system where it would have gone had it not been reused. Greywater should be pumped into the toilet bowl for flushing. DO NOT put greywater into the toilet tank.
What can I use grey water for? ›The easiest way to use greywater is to pipe it directly outside and use it to water ornamental plants or fruit trees. Greywater can also be used to irrigate vegetable plants as long as it doesn't touch edible parts of the plants.
What is domestic grey water treatment? ›Typically, aerobic and biological treatments are used as primary greywater treatment to remove dissolved and suspended biological matter, followed by ultra-filtration to prevent particles, bacteria and viruses of passing through.
How much greywater per person per day? ›The average person produces around 100 litres of greywater per day1. This amounts to 146,000 litres per year for a family of four.
How can I reuse greywater at home? ›In California, homeowners are now allowed to irrigate with untreated water straight from bathroom sinks, washing machines and bathtubs, as long as — among other requirements — the water lines run beneath soil or mulch, so as not to come in contact with people.
Can you reuse grey water for shower? ›Or, you can invest in a greywater pump unit to take the water away from, for example, your washing machine, bath, shower and kitchen sink. It can then sit in a tank where it's chemically treated by adding chlorine. It's then sent to wherever it's needed e.g. washing machine or the toilet cistern.
Can I put grey water down the drain? ›Grey waste is shower and sink dirty water and black waste is toilet waste. In most places, you can't dispose of them in the same place. Grey water goes down a drain and black waste goes into a chemical toilet disposal point.
Is greywater water from sinks tubs and toilets? ›Greywater: is the wastewater that comes from sinks, washing machines, bathtubs and showers. It contains lower levels of contamination, making it easier to treat and process. Recycled greywater is commonly used in irrigation and constructed wetlands – as long as no harmful chemicals are present.
Is shower water grey water? ›Gray water is defined as household wastewater that comes from showers, laundry water, bath water, lavatory (basin) water, and untreated spa water.
Is dishwasher water grey water? ›
What is Greywater? Greywater is wastewater from bathtubs, showers, bathroom sinks, washing machines, dishwashers, and kitchen sinks - any source other than toilets and urinals.
Can you filter and drink grey water? ›Keep in mind that even though the filtered greywater looks clear, it's not potable and shouldn't be consumed by animals.
What are the three types of grey water systems? ›There are three types of greywater systems - Laundry-to-Landscape (L2L), Simple, and Complex greywater systems.
What size pipe for greywater? ›1.5” ABS pipe and fittings were used throughout to transport the water. The pipe sizes are relatively large to avoid any possible clogs (there will be some hair and soap moving through the pipe). The pipe and fittings are inexpensive and easy to get at any big box supply store.
What are the two types of grey water systems? ›There are basically two types of graywater systems: gravity fed manual systems and package systems. The manual systems do not require electricity or pumps because they work on gravity taking the graywater to the area needed. They may require a larger yard area to install the system outside.
How do you calculate GREY water footprint? ›The process grey water footprint, WF proc, grey [s] (m3/year) is calculated by dividing the pollutant load (kg/year) by the difference between the ambient water quality standard for that pollutant (Cmax, in kg/m3) and its natural concentration in river (surface water) (Cnat, in kg/m3) [23].
How do you calculate GREY water? ›The grey component in the Water Footprint of growing a crop or tree (WFproc,grey, m3/ton) is calculated as the chemical application rate per hectare (AR, kg/ha) times the leaching fraction (α) divided by the maximum acceptable concentration (cmax, kg/m3) minus the natural concentration for the pollutant considered ( ...
What are the disadvantages of greywater? ›All greywater has the potential to harbor dangerous bacteria and viruses. It is never potable. Micro-organisms present in untreated greywater can cause damage to foliage. Untreated greywater should not be used for lawn sprinklers, as this could spread dangerous, airborne bacteria.
How do you disinfect greywater? ›Clean the filter much the same way you would clean a pool filter, by clearing out the debris and then rinsing. You can also add a few teaspoons of bicarbonate of soda to some warm water and a splash of vinegar and you have a non-toxic deodorizing and cleaning solution.
Is rain water grey water? ›Rainwater collection and greywater reuse are wonderful ways to nourish a garden while making the most out of every last drop of water. But it's important to understand that rainwater and greywater are not the same.
Can you water vegetables with greywater? ›
It can be safely used to water trees, gardens, vegetables and lawns.
Does grey water turn to black water? ›While this water shouldn't be used for cooking or drinking, some people choose to recycle it to water their lawns and flower beds. However, it is important to understand that greywater can turn into blackwater in as little as 48 hours.
Can you use grey water for washing machine? ›Graywater, or greywater, is lightly used household water from clothes washing machines, showers, bathroom tubs, and bathroom sinks.
How do you use grey water in the winter? ›Diverting greywater to an attached greenhouse reduces the risk of frozen pipes, creates a heat sink (warm greywater) to heat the house all winter long, and provides water to winter gardens. Indoor and greenhouse systems should be well drained and ventilated to avoid mold-promoting damp conditions.
Can kitchen sink go to greywater? ›It's important to understand which chemicals go down household drains, as you don't want to use gray water with elevated levels of chlorides, sodium, borax or sulfate that has a high pH, which could be harmful to your plants. Gray water does not include water from a kitchen sink, dishwasher or toilet.
Do you drain black or grey water first? ›Dump the black water tank first, then the gray tank. Dumping the gray tank last helps flush out the sewer hose. After you dump both tanks, thoroughly flush out the tanks. Some RVs have a built-in system for flushing.
Can grey water go into soil pipe? ›Soil Pipes are designed to transport the soiled water (blackwater) from your toilet, urinal, or bidet (if you're fancy). Waste Pipes are designed to transport the wastewater (greywater) from your sinks, shower, bath, washing machine, or dishwasher.
Is the water from a kitchen sink considered blackwater or greywater? ›Greywater is gently used water from sinks, showers, baths, and washing machines; it is not wastewater from toilets or laundry loads containing poopy diapers.
Is bathroom sink water OK? ›Your bathroom tap water is perfectly fine to brush your teeth and to wash up. As long as you're not swallowing the water, you're unlikely to get lead poisoning.
Is water from bathroom sink same as kitchen? ›Is water from bathroom sink same as kitchen? Yes. Same water from the same source coming into the building. And yes, it fills the tub, the shower, dishwasher, and even the toilet.
What laundry detergent is best for grey water? ›
Oasis and Ecos are a two great brands we are aware of. These are the gold standard of greywater irrigation. They have the lowest number of ingredients and the fewest sodium compounds (none for Oasis, one for Ecos) – with no synthetic additives to speak of.
Why does gray water smell? ›The water from a greywater tank will always have a slight odor due to the small waste particles in it which form sludges and stagnate over time. However, the smell should not be pungent and is best kept in check by regular pump out and cleaning of the greywater tank and the grease trap.
Is gray water good for Plants? ›As long as you're only putting biodegradable products down the drain, graywater is perfectly safe for irrigating plants. Kitchen sink water is technically considered graywater as well, but because of its grease content it often requires additional treatment before being used for irrigation.
Can I water my plants with laundry water? ›If your home does not have a water softener, your bathwater and rinse water from dishes and laundry are all of good quality for irrigation. Soapy wash water from dishes and laundry might better be saved to flush the toilet, but can be used for irrigation if you're careful about certain possible problems.
What dish soap is gray water safe? ›A pure castile soap, such as Dr. Bronner's, is perfect for greywater as is Oasis dish or all purpose cleaner.
Is it OK to water plants with soapy water? ›It allows us to preserve beneficial insects in the garden. It also means that not every insect will be bothered by soap. Small, soft-bodied insects are the best candidates for management with soapy water. Aphids, whiteflies, thrips, and mites are all good candidates for soapy water sprays.
How do you make grey water drinkable? ›Natural fibrous components — like activated charcoal powder, moringa oleifera seeds, and crushed corn cob — have the potential to purify greywater. Greywater treatment is a method to reuse used water and save freshwater resources for drinking purposes.
How long can greywater be stored? ›Greywater Guidelines
Greywater should not be stored for more than 24 hours. If the greywater is stored for too long, the nutrients will begin to break down and the water will emit an unpleasant odor.
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To build a DIY greywater system for your home, install a diverter valve and a pipe to divert water from your washing machine through a filter. Next, add plumbing from the filter to a storage tank, put a valve with a spigot on the tank, and choose a greywater dispensing method.
Can sand filter grey water? ›
Sand filters are becoming popular and have been achieving economic efficiency in greywater treatment for reuse in households and for irrigation in regions of water shortage [18,19].
What is the difference between grey water and waste water? ›Blackwater refers to wastewater from toilets, whereas greywater refers to wastewater from sinks, dishwashers, bathtubs, and washing machines. Blackwater contains disease-carrying bacteria, whereas greywater contains fewer contaminants.
What is the slope for greywater drain? ›Gravity-fed greywater distribution plumbing, such as branched drain systems, should maintain a minimum 2% slope (1/4-inch drop per linear foot or 2-cm drop per linear meter).
What is the grey water pipe called? ›Polybutylene pipe is a gray plastic tubing that was commonly used as a water-supply plumbing pipe between 1978 and 1996, at which time it was discontinued due to reports of pipes rupturing. 1 In new construction, it was replaced by copper or more dependable forms of plastic pipe, such as CPVC and PEX.
How far down should a water pipe be? ›Avoid freezing pipes
According to 'The Department of the Environment', they recommend that pipes should be buried at least 600mm (two feet) underground. At this depth, the soil acts as a natural insulator and prevents them freezing.
Graywater includes wastewater from bathtubs, showers, bathroom wash basins, clothes washing machines, laundry tubs, or an equivalent discharge as defined by the Los Angeles Department of Public Health. It does not include wastewater from kitchen sinks, photo lab sinks, dishwashers, or laundry water from soiled diapers.
What is a household greywater treatment system? ›Aqua2use greywater systems for residential homes use wastewater from your washing machine, shower and bath. The soapy residue in the draining water makes the water appear grey, but once filtered through our system it appears clear, just like regular drinking water. Although the water appears safe to drink, it isn't.
What are the harmful effects of greywater? ›For some other variables such as boron and surfactants, greywater may even be of worse quality than wastewater. Long-term irrigation of arid loess soil with greywater may result in accumulation of salts, surfactants and boron in the soil, causing changes in soil properties and toxicity to plants.
What are the consequences of grey water? ›Key nutrients in grey water can fuel harmful algal blooms (HABs), which cause mass ecosystem dysfunction by producing toxins, blocking sunlight and clogging fish gills. After the bloom dies, the process of decomposition consumes locally available oxygen, creating marine dead zones.
Does greywater have bacteria? ›Due to the limited treatment technology, the treated greywater still contains some chemicals and bacteria, so some safety issues should be observed when using the treated greywater around the home.
Is grey water a biohazard? ›
Grey water can certainly harm the environment. While grey water isn't a biohazard like raw sewage, it still contains substances and bacteria that aren't native to the environment.
What contaminants are in greywater? ›For most households greywater contains soap, shampoo, toothpaste, shaving cream, laundry detergents, hair, lint, body oils, dirt, grease, fats, chemicals (from soaps, shampoos, cosmetics) and urine1. The most significant pollutant of greywater is laundry detergent, particularly those high in sodium and phosphorus.
Is it safe to water vegetables with greywater? ›Because grey water can contain bacteria and viruses that cause illness, it should not be used to grow vegetables if the edible portion may come in contact with the soil.
What pollutants are in greywater? ›Kitchen waste are the primary source of nitrogen in greywater and range between 4 and 74 mg/L while washing detergents are the primary source of phosphates found in grey water which also range between 4 and 14 mg/L (Boyjoo et al.
What are the different types of greywater systems? ›There are basically two types of graywater systems: gravity fed manual systems and package systems. The manual systems do not require electricity or pumps because they work on gravity taking the graywater to the area needed. They may require a larger yard area to install the system outside.
Why does grey water need to be filtered? ›Greywater removes large contaminants from water, like hair, dirt, and grass. One obstacle with standard filters is they are unable to refine excess salts, chemicals, and minerals that may pollute the water.
What is the difference between gray water and contaminated water? ›Greywater: is the wastewater that comes from sinks, washing machines, bathtubs and showers. It contains lower levels of contamination, making it easier to treat and process. Recycled greywater is commonly used in irrigation and constructed wetlands – as long as no harmful chemicals are present.
Is bleach safe for greywater? ›Toxic discharges such as rinse water from paint, chlorine bleach, or hair dye should never be released into the greywater system.
Is washing machine water considered grey water? ›What is graywater? Graywater, or greywater, is lightly used household water from clothes washing machines, showers, bathroom tubs, and bathroom sinks. It does not include waste water from toilets, kitchen sinks, dishwashers, or laundry water with soiled diapers.
Is sink considered grey water? ›“Greywater” is domestic wastewater that's drained from household sinks, showers, bathtubs, and washing machines. Unlike water in septic pipes, it's a resource that can be treated and filtered and then reused.