Grey Water Recycling
What are they?
Grey water recycling typically involves the capture of water previously used in bathroom sinks and showers and storing it for flushing toilets, cooling tower ,make-up and irrigation of external planting and green roofs / walls. Grey water is filtered and stored in a tank at ground or basement level, or buried underground. The water is not of a potable standard and therefore is not used to serve sinks.
Grey water recycling and rainwater harvesting systems can be combined to reduce even further the amount of potable water consumed for flushing and irrigation.
Advantages / Disadvantages
Reduces the amount of potable water used. This also reduces CO2emisions as treating water to potable standard and pumping it are energy intensive.
Strong sustainability message.
Only effective if installed in a building where large quantities of grey water are produced and where there is a significant flushing / irrigation demand.
Grey water treatment is a specialist field that requires careful management and maintenance.
The volume of water saved depends on the number of appliances water is being collected from, the ability to store it hygienically until it is needed and a high demand for non-potable water.
Grey water recycling reduces water supply and waste water bills which will offset any additional maintenance costs providing water collection and flushing / irrigation demand is high.
Retrofit / improvement opportunities
Retrofit is expensive and disruptive because a dual run of pipe-work is required to collect the grey water from sinks and showers throughout the building. A large tank and filtering equipment also needs to be accommodated.
Not typically suited for commercial buildings because the amount of available grey water produced is low. Well suited to gymnasiums (shower water) especially if the water can be exported to other users,
Floor plate implications
Periodic cleaning and replacement of water filters is required. These are more onerous when compared to a rainwater harvesting system.
A large tank is situated at ground or basement level and a grey water treatment unit.
Questions to ask
- Is there a grey water harvesting system in place?