What is greywater ?
Any wash water that has been used in the home, except water from toilets, is called greywater . Dish, shower, sink, and laundry
water comprise 50-80% of residential "waste" water. This may be reused for other purposes, especially landscape irrigation
Why use greywater ?
It's a waste to irrigate with great quantities of drinking water when plants thrive on used water containing small bits of
compost. Unlike a lot of ecological stopgap measures, greywater reuse is a part of the fundamental solution to many ecological problems and will probably remain essentially unchanged in the distant future. The benefits of greywater
- Lower fresh water use
- Less strain on failing septic tank or treatment plant
- Better treatment (topsoil is many times more effective than subsoil or treatment plant)
- Less energy and chemical use
- Groundwater recharge
- Plant growth
- Reclamation of otherwise wasted nutrients
- Increased awareness of and sensitivity to natural cycles
Why Does Greywater Matter?
Viewed narrowly, greywater systems don’t look that important. A low flow shower head can save water with less effort. A
septic system can treat greywater almost as well.
But when you look at the whole picture, how everything connects, the keystone importance of greywater is revealed.
- Ecological systems design is about context, and integration between systems. The entirety of
integrated, ecological design can be reduced to one sentence: do what's appropriate for the context.
- Ecological systems such as rainwater harvesting, runoff management, passive solar, composting toilets, edible landscaping; all of these are more context sensitive than their counterparts in conventional
practice; that's most of what makes them more ecological.
- Greywater systems are more context sensitive than any other manmade ecological system, and more connected to more other systems.
- Get the greywater just right, and you’ve got the whole package right, and that is what matters.
- Many people and organizations instinctively recognize that greywater is the ideal test case for the transition to a new way of
regulating and building that is appropriate to a post-peak resource, mature civilization.
The US Green Building Council, the City of Santa Barbara, CA, Oregon ReCode, and SLO Green Build are among those organizations
which independently chose greywater standards as the technology with which to launch their programs of regulatory reform.
Is greywater reuse safe?
Yes. There are eight million greywater systems in the US with 22 million users. In 60 years, there has been one billion system
user-years of exposure, yet there has not been one documented case of greywater transmitted illness.
Water recycling systems without purification
Water diversion systems
The simplest greywater system is to simply divert the water directly to the garden. Regulations change by country and region, but
common guidelines for safe usage include not storing the greywater for more than 24 hours, ensuring it cannot pool or run off, and depositing it with subsurface irrigation.
Greywater diversion systems can be both designed-in to new homes, or retrofitted to many existing homes. When systems are fully
designed, manufactured and installed to relevant standards such as the Australian Watermark standards. Water diversion systems tend to be highly efficient, effective and safe for simple applications where potable water is not required.
Diversion systems can be as basic as running the outlet hose from a washing machine out a window to the garden, or can be designed
as a permanent part of the home plumbing. Fully engineered systems incorporate a sump pump and surge tanks and deliver the water through sub-surface irrigation.
Greywater from the shower or bath is generally good quality water for the garden. The soap levels at the dilution levels typical
are actually good for the garden as they are a wetting agent. When laundry greywater is diverted to the garden then the laundry products must be chosen carefully to ensure phosphate and salt levels are low, and the pH balance is neutral.
Basic guidelines are also available from system suppliers. It is essential that greywater is diverted to sewer when
garden-unfriendly products are being used.
Water recycling with purification
For filtering the water to become potable (or near-potable), there are numerous systems based on soft processes. These include natural biological principles such as
- mechanical systems (sand filtration, lava filter systems and systems based on UV radiation)
- biological systems (plant systems as treatment ponds, constructed wetlands, living walls) and compact systems as activated sludge
systems, biorotors, aerobic and anaerobic biofilters, submerged aerated filters, biorolls
- Finally, also used for creating potable (or near-potable) water are the "hard", direct processes, such as distillation
(evaporation). There seem to be no commercially available "hard" greywater recovery devices suitable for on-site use in the individual household, even though a number of such technologies exist.
In order to purify the water adequately, several of these systems are usually combined to work as a whole. Combination of the
systems is done in two to three stages, knowingly a primary and a secondary purification. Sometimes a tertiary purification is also added.
Some municipal sewerage systems recycle a certain amount of grey- and blackwaters using a high standard of treatment, thus
providing reclaimed water for irrigation and other uses.
Application of recycled greywater
Greywater typically breaks down faster than blackwater and has lower levels of nitrogen and phosphorus. However, all greywater must
be assumed to have some blackwater-type components, including pathogens of various sorts. Greywater should be applied below the soil surface where possible (e.g., in mulch-filled trenches) and not sprayed, as there is a danger of
inhaling the water as an aerosol.
Long-term research on greywater use on soil has not yet been done and it is possible that there may be negative impacts on soil
productivity. If you are concerned about this, avoid using laundry powders; these often contain high levels of salt as a bulking agent.
In any greywater system, it is essential to put nothing toxic down the draino bleaches, bath salts, artificial dyes, cleansers,
shampoos, and no products containing boron (which is toxic to plants at high levels).
It is crucial to use all-natural, biodegradable soaps whose ingredients do not harm plants. Most powdered detergents, and some
liquid detergents, are sodium-based, which can inhibit seed-germination and destroy the structure of clay soils.
"Natural" body products often contain substances toxic to humans, including parabens, stearalkonium chloride,
phenoxyethanol, polyethelene glycol (PEG), and synthetic fragrances.
Recycled greywater from showers and bathtubs can be used for flushing toilets in most European and Australian jurisdictions and in
United States jurisdictions that have adopted the International Plumbing Code.
Such a system could provide an estimated 30% reduction in water use for the average household. The danger of biological
contamination is avoided by using:
- a cleaning tank, to eliminate floating and sinking items
- an intelligent control mechanism that flushes the collected water if it has been stored long enough to be hazardous; this completely avoids the problems of filtration and chemical treatment
Because greywater use, especially domestically, reduces demand on conventional water supplies and pressure on sewage treatment
systems, its use is very beneficial to local waterways. In times of drought, especially in urban areas, greywater use in gardens or toilet systems helps to achieve the goals of ecologically sustainable development.
The potential ecological benefits of greywater recycling include:
- Lower fresh water extraction from rivers and aquifers
- Less impact from septic tank and treatment plant infrastructure
- Topsoil nutrification
- Reduced energy use and chemical pollution from treatment
- Groundwater recharge
- Increased plant growth
- Reclamation of nutrients
- Greater quality of surface and ground water when preserved by the natural purification in the top layers of soil than generated water treatment processes
- In the U.S. Southwest and the Middle East where available water supplies are limited, especially in view of a rapidly growing
population, a strong imperative exists for adoption of alternative water technologies.
Potential downsides of greywater recycling
The Southern Nevada Water Authority has expressed concern that greywater recycling for use in residential washing machines and for
watering xeriscapes could encourage greater water use, and reduce the amount of water returned to Lake Mead, a reservoir currently experiencing a drought.
Greywater users and advocates dispute these claims.
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