Case study: greywater

In 1997 Essex & Suffolk Water worked with the Building Research Establishment (BRE)33 involving a small development of new Housing Association Homes in Heybridge, Essex34. Three houses had greywater systems installed. The Water Dynamics Well Butt System takes water from the bath and bathroom hand basin and filters and disinfects it (by passing it through aqua bromide tablets). This water is then used to flush toilets.
The systems were installed at a cost of £1286. Each property had a different number of people living in them and this produced varying results:

Property type	Total occupancy	Property composition	% of time the system worked	Potable water saved (%)
3 bedroom end of terrace	3	1 adult, 2 teenagers	63%	53%
3 bedroom terrace	3	1 adult, 2 teenagers	83%	65%
4 bedroom end terrace	7	2 adults, 3 teenagers and 1 under 5	39%	24%

Essex and Suffolk Water identified a number of factors that determined how much water was saved by properties as a result of installing a greywater system:

• unexpected failure of the system components during the trial reduced water saved;
  
• lifestyle patterns influenced the amount of water saved. The family of seven usually
  all bathed on a Saturday night, generating enough greywater for WC flushing up to the end of the following Tuesday. This routine of bathing at weekends only, combined with how much water the tanks hold, did not supply enough greywater for WC flushing for a full week.
  As well as looking at the savings, the study also analysed the greywater quality. Samples were taken from three locations and the following observations were made:
  
• collection tank – low faecal indicator organisms suggested the absence of pathogens. No legionella was detected;
  
• WC cistern – showed the treatment process was effective as only a low number of coliforms were present, indicating the absence of any pathogens; and
  
• header cistern – similar observations to the WC cistern.
  It was noted that the turbidity of the water increased over time in some of the collection
  tanks, suggesting that there is a need for regular cleaning and disinfecting. 

http://cdn.environment-agency.gov.uk/geho0511btwc-e-e.pdf