Report No DWI0779

WATER CONSERVATION: IMPLICATIONS OF USING RECYCLED GREYWATER AND STORED RAINWATER IN THE UK

Final Report 13034/1

DWI0779

Mar 1997

EXECUTIVE SUMMARY

This report details the results of research into the implications of using recycled greywater and stored rainwater in the UK. A number of proprietary systems are available on the market worldwide and several are produced by UK manufacturers. Not all those produced overseas are appropriate for use in the UK. Many of the greywater recycling systems sold in the USA, for example, are designed for direct sub-surface landscape irrigation, an application currently of limited applicability in the UK. Some of the systems currently produced or under development by UK manufacturers have significant potential to achieve substantial market penetration in the UK and overseas.

An important constraint on the uptake and use of greywater reuse and stored rainwater systems in the UK is their perceived risk to public health. This is particularly so for greywater recycling systems, as there is a possibility that greywater, having been in primary or secondary contact with humans, at least once before reuse, may contain low levels of faecal contaminants. Health considerations have led a number of authorities outside the UK to severely restrict the types of greywater recycling system that are permitted. However, due to recent advances in wastewater treatment technology, experience gained elsewhere, and because public health risks are very application-specific, similarly restrictive regulations on the end-use of recycled water may not be required in the UK. Instead it is suggested that individual systems should be tested to a previously determined standard by an accredited test-house before they can be sold or installed, and that water quality criteria should be application specific.

Suitable water quality standards for the UK are proposed in this report, based on relevant standards from the UK and overseas. Additionally, general UK requirements are included for the design, construction, operation and maintenance of systems necessary to protect public health and minimise deleterious effects to plumbing systems and the environment.

User/social acceptability is unlikely to discourage the uptake and use of systems in the UK. Published reports from overseas and reported experiences concerning the limited number of systems already installed in the UK, suggest that user/social acceptability will not be a problem if systems are appropriately designed and operated.

The report includes a comprehensive economic analysis of the application of recycled greywater and stored rainwater systems in five building types, using six generalised system types, two toilet cistern sizes and both new-build and retrofit situations. Of the building types considered, hotel installations appear to yield the shortest pay-back periods. An important conclusion is that for systems to be economically viable, it is not necessary that they should be designed to utilise a large percentage of the rainwater or greywater available, as this increases the cost of storage provision.

It is difficult to predict the degree to which greywater and stored rainwater technologies will be utilised in the UK. However, the use of such systems would undoubtedly become increasingly attractive if water charges were raised or if a recognised system of accreditation were introduced, to verify the safety and performance of such systems.

Copies of this report may be available as an Acrobat pdf download under the 'Pre 2000 Reports' heading on the DWI website.