Cequesta - Commercial and Domestic Water Recycling technology

Any water that has been used except for toilets or cooking  is called grey water. Dish, shower, sink, and laundry water comprise 50-70% of residential "waste" water. This may be reused for flushing, washing, or irrigation and gardens.

Water engineers like to define waste water as either black or grey. Black requires sophisticated treatments before it can be released into the sewage system. By contrast, grey water has lower levels of impurities generally measured by Biological Oxygen Demand – BOD and Suspended Solids – SS.

The diagram shows the distribution of water use in a household.  Black water  goes to the local treatment works where it can be recycled for agricultural use only.  Grey water is reused on the spot. The more grey water is recycled, the less municipalities need to expand their water supply system – this is of crucial importance for many third world cities.


Buildings which can reuse their grey water must have separate plumbing for ‘black’ and ‘grey’ waters. See appendix 1 for a more detailed explanation.