What is Gray Water

Posted by Chris Hill on

What is Gray Water?

Gray water is defined as household wastewater that comes from showers, laundry water, bathwater, lavatory (basin) water, and untreated spa water but doesn’t include toilet, kitchen sink, or dishwasher waste.(water from the kitchen (kitchen sink) is not recommended for reuse due to the high levels of organic materials such as oils and fats.) Grey water may be re-used for low-risk.
Gray water, also spelled as grey water, is water that already has been used domestically, commercially and industrially. This includes the leftover, untreated water generated from clothes washers, bathtubs and bathroom sinks.

Rather than wasting Graywater can we recycle it?

The short answer is yes. One of the most widely used methods of recycling gray water is to capture it and use it on plants and gardens. There are other methods for recycling, but a residential graywater recycling system can cost $10,000 or more.

In an urban situation, with a utility provided sewage system, we recommend only re-using shower, bath, spa bath and laundry water. Kitchen and lavatory water is best left for the blackwater waste pipe network. Lavatory water is in most cases does not provide enough water to justify the connection cost, and in any case, provides additional water flow to help flush the blackwater pipe system.

In a rural situation (i.e. a septic system is used), kitchen water can be used (subject to local regulations), IF the following occurs:
A grease trap is installed between the kitchen sink and the graywater system. This ensures food scraps, fats and oils are irrigated in the garden. In addition to containing high bacteria levels, the significant quantity of fats can create an impervious barrier within the topsoil.
The dishwasher does not empty into the kitchen sink waste because the detergent is too caustic.
Gardens do not need clean potable water to flourish. In fact many times they thrive on the nutrients that are found in gray water.

Is gray water dangerous?

Graywater (also known as “greywater”) has the potential to carry bacteria and viruses, making it unsafe to drink. In short, greywater is never potable. However, it can be used for things like flushing toilets and subsurface irrigation of lawns, ornamental gardens.
Untreated, greywater can be unsafe for irrigation via sprinklers as it may cause bacteria and viruses to become airborne.
However, some household water, such as wastewater from toilets, kitchen sinks, dishwashers, or laundry water from soiled diapers, is not suitable for reuse because it may contain bacterial contaminants, grease or residues of detergents that are harmful to plants.
Similarly, greywater cannot be used to irrigate root crops or other edible crops that touch the soil. But greywater is fine for watering fruit trees and landscaping plants.
This water source is a common way to recycle water and stretch urban water supplies. As part of this, gray water ‘harvesting’ (the collecting of gray water from sinks, showers, etc.) is increasingly popular.

How does grey water differ from sewage (black water)?

Both grey water and black water are types of wastewater. Grey water is the result of water being used for household purposes, like bathing and washing clothes, while black water contains feces and urine and other bodily wastes. Grey water can be recycled as its bacterial count is much lower than black water, including the presence of pathogens. Accordingly, black water typically needs more intensive treatment to kill the disease carrying bacteria present. Recycled grey water also tends to turn into black
water after use, as it can be used to flush toilets.

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