What is grey water?
Any water that has been used in the home, except water from toilets, is called grey water. Dish, shower, sink, and laundry water comprise 50-80% of residential "waste" water. This may be reused for other purposes.
The key challenge is to separate grey water from black water (toilet water) in the collecting of different waste water as well as the supply of different water qualities (drinking water for kitchen, shower or recycled water for toilet, washing machine etc) into the distribution system.
Why use grey water?
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, grey water reuse is a part of the fundamental solution to many ecological and water availabillity problems and will probably remain essentially unchanged in the distant future. The benefits of grey water recycling include:
- Lower fresh water use
- Easy water reuse/recycling
- Cheap indoor/Outodoor multiple recycling systems available
- Less strain on failing septic tank or treatment plant
- Grey water treatment to any kind of desired quality
- Ability to build in areas unsuitable for conventional treatment
- Less energy and chemical use
- Groundwater recharge
- Plant growth
- Reclamation of otherwise wasted nutrients
The benefits of grey water recycling (in detail)
* Lower fresh water use
Grey water can replace fresh water in many instances, saving money and increasing the effective water supply in any regions. Residential water use is almost evenly split between indoor and outdoor. All except toilet water could be recycled indoors or outdoors, achieving the same or even better results then public systems with significantly less water diverted from nature.
* Less strain on septic tank or treatment plant
Grey water use greatly extends the useful life and capacity of septic systems. For municipal treatment systems, decreased wastewater flow means higher treatment effectiveness and lower costs.
* Highly effective purification
Grey water can be easier purified to a spectacularly high degree with a number of technical or biological treatments systems.
* Site unsuitable for a septic tank
For sites with slow soil percolation or other problems, a grey water system can be a partial or complete substitute for a very costly, over-engineered system.
* Less energy and chemical use
Less energy and chemicals are used due to the reduced amount of both freshwater and wastewater that needs pumping and treatment. For those providing their own water or electricity, the advantage of a reduced burden on the infrastructure is felt directly. Also, treating your wastewater in the soil under your own fruit trees definitely encourages you to dump fewer toxic chemicals down the drain.
* Groundwater recharge
Grey water application in excess of plant needs recharges groundwater.
* Plant growth
Grey water enables a landscape to flourish where water may not otherwise be available to support much plant growth.
* Reclamation of otherwise wasted nutrients
Loss of nutrients through wastewater disposal in rivers or oceans is a subtle, but highly significant form of erosion. Reclaiming nutrients in grey water helps to maintain the fertility of the land.
* Increased awareness of and sensitivity to natural cycles
Grey water use yields the satisfaction of taking responsibility for the wise husbandry of an important resource.
Matching quality/quantity with actual requirements
Not all water required in household, municipal or commercial applications has to have drinking water quality. Separating the different quality requirements you will find huge saving potentials in recycling grey water and reusing it over and over again.
Avoiding large infrastructural costs and problems
A larger number of small scale grey water recycling solutions will not only reduce the costs and burden of large infrastructural program, it will also increase the flexibility and the robustness of its proper functioning.
Other information / Definitions
Household wastewater (according to DIN EN 1085)
Wastewater from kitchens, washing machines, bathrooms, toilets and similarly used rooms.
Blackwater
Blackwater is part of the household wastewater. It is the drain from toilets and therefore, contains urine and/or faeces.
Greywater
Greywater is a part of the household wastewater without blackwater. It is the drain from bath tubs and shower trays, washbasins and washing machines and may also contain high-strength kitchen wastewater.
Water for greywater recycling
The least concentrated flows of the available household wastewater are especially appropriate for greywater recycling. For residential buildings, these are the drains from bath tubs and shower trays as well as washbasins. Under certain conditions, the use of the washing machine drain or even kitchen wastewater may be of significance.
Greywater recycling plant
A plant which collects greywater and treats it to process water of sufficient quality for specific reuse purposes.
Process water
According to DIN 4046, process water is defined as ?water with different quality characteristics serving commercial, industrial, agricultural or similar purposes?. In connection with greywater recycling, it also includes water which is used in households and trade and which does not have to be of a drinking water quality, such as water used for toilet flushing, irrigation, for cleaning purposes or for laundry.
Energy consumption
Less then 1,2kWh/m³ of treated grey water plus pressure increase which is around 0,8 kWh/m³
Guarantee
Within 15 years free of charge replacement of any earth tanks.
Download DWC Fundamentals on Grey Water Recycling (6 pages, pdf, english)
