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.

Water efficiency

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.

Running costs

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.

Applicable buildings

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


Occupant comfort

None generally.

Maintenance 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?