DomesticGreywater Reuse: Overseas Practice and its Applicability to Australia
ReportNo WSAA 73
Thisreport is the second on a research project to determine the potential fordomestic greywater re-use in Australia.
Thefirst report, “Domestic Greywater Re-use:Preliminary Evaluation (UWRAA Research Report No 60)”, was based onoverseas correspondence, a literature search, and chemical and microbialanalysis of some sullage systems. That report concluded that the western statesof the USA and Japan are the world leaders in this type of onsite re-use andthat greywater re-use poses environmental and health concerns but, withadequate guidelines, could achieve substantial water savings. This secondreport investigates overseas practices in greywater re-use and how thesepractises could apply to Australia.
Domesticwastewater can be segregated into two separate flows, namely:
Although toilet wastes are excluded fromgreywater, greywater still contains human faecal indicator bacteria inconcentrations high enough to indicate a health risk from the potentialpresence of pathogenic micro organisms. Overseas authorities have confirmedthis conclusion.
Forsafe re-use, either of the following must occur:
Treatmentof greywater to make it safe for human contact is expensive to achieve on anindividual household basis. It is also difficult to ensure that treatmentsystems are maintained. Surveys in the USA, Australia and Brisbane have foundthat 60% to 80% of “onsite domestic wastewater treatment plants” are notmaintained adequately. These treatment plants consistently do not produce anacceptable quality effluent.
Limitedevidence from trials and existing greywater systems suggests that there are noadverse effects on lawns and ornamental gardens from chemicals occurring ingreywater. However concerns are raised that chemicals in greywater could causedamage to clay soils and some native plants and increase the levels ornutrients in groundwater and waterways.
Thetwenty-two Western States of the USA allow the direct re-use of untreateddomestic greywater by sub-surface watering of ornamental gardens and lawns. Toprevent human contact with untreated greywater, sub-surface techniques, such assub-surface drip emitters and leach fields, are specified.
Toiletflushing with greywater is not allowed because of the risk of human contact(from splashing and aerosols) and the unreliability of household treatment. The preliminary evaluation given in thefirst report wrongly concluded that greywater re-use for toilet flushing didnot require treatment other than disinfection and coarse screening.
Japandoes not re-use greywater, except for hand washing water (without soap) beingre-used to flush toilets. However, the Japanese carry out wastewaterreclamation for toilet flushing, irrigation, and ornamental ponds/fountains,using expensive and sophisticated treatment processes. This happens in highrise buildings and at regional treatment plants and, because of Japan’s severewater shortage, is economical.
Thethird and final part of the research will include testing and evaluation ofexisting sullage systems to determine guidelines for the application ofdomestic greywater re-use for Australia. Trials will also be carried out onhand basin cisterns which re-use hand washing water for toilet flushing.
Copiesof the Report are available from WSAA, price $A50. Orders may be placed throughthe Bookshop at www.wsaa.asn.au or by email to email@example.com.