Using rainwater and grey-water to reduce fresh-water consumption

©Mr Twister, image #92827682, 2017, source:


Investment cost:
Medium cost
Cost savings:
For a company of 100 employees using rainwater for flushing toilets, savings depend on the water efficiency of WCs and costs for fresh-water and sewage Savings for grey-water recycling largely depend on local conditions (e.g. suitable grey-water, possible uses)
Payback time:
Equipment costs in water-recycling facilities are generally higher and the payback period longer than for other water-efficiency measures (achievable savings for grey-water recycling are higher than for rainwater recycling) Water costs and waste-water treatment fees vary greatly in different regions and this has an impact on economic feasibility
Medium cost
Size of company:
Micro (less than 10)

Rainwater and grey-water can be used instead of fresh-water in a number of applications, including toilet flushing, cleaning and irrigation, which reduces fresh- and waste-water volumes and corresponding costs. 

Grey-water is slightly polluted waste-water e.g. from showers or production. It can be easily treated and reused in different processes. Rainwater can be used in, for example, fire-fighting reservoirs, as cooling water or in heating systems. Rainwater can be collected from roof-tops, filtered and stored in reservoirs. Rainwater also contains no chalk, so less detergent or chemicals are needed when used for cleaning.

Using rainwater and grey-water can reduce the cost of fresh-water as well as for sewage. In addition to water-efficiency measures, water recycling can reduce fresh-water consumption by about 10 %, which has financial and environmental benefits, especially in water-poor regions trying to mitigate the impacts of climate change. 

The installation of rainwater and grey-water recycling systems is applicable to all new buildings. Retrofitting such systems to existing buildings is expensive and impractical unless the building is undergoing extensive renovation. Building ownership is also an issue for the renovation of buildings with these systems.

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