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Application for Greywater
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Irrigation, Indoor reuse, Extreme living conditions, Heat reclamation

Greywater typically breaks down faster than blackwater and has much less nitrogen and phosphorus. However, all greywater must be assumed to have some blackwater-type components, including pathogens of various sorts. Greywater should be applied below the soil surface where possible (e.g. in mulch filled trenches) and not sprayed, as there is a danger of inhaling the water as an aerosol.

However, long term research on greywater use on soil has not yet been done and it is possible that there may be negative impacts on soil productivity. If you are concerned about this, avoid using laundry powders; these often contain high levels of salt as a bulking agent, and this has the same effect on your soil as a drought.

Indoor reuse

Recycled greywater from showers and bathtubs can be used for flushing toilets in most European and Australian jurisdictions, and in US jurisdictrions adopting the International Plumbing Code. A commercial example would be Ecoplay . It is estimated that such a system could provide a 30% reduction in water use for the average household. The danger of biological contamination is avoided in two ways. Firstly a cleaning tank in used to elimate floating and sinking items. Secondly an intelligent control mechanism flushes the collected water if it has been stored long enough to be hazardous. By doing this it completely sidesteps the problems of filters or chemical treatment. US Jurisdictions adopting the Uniform Plumbing Code may not use greywater indoors.

Extreme living conditions

Greywater use promotes the ability to build in areas unsuitable for conventional treatment, or where conventional treatment is costly. The Mars Desert Research Station utilizes greywater recycling for this use, and might be used on trips to Mars to reduce water consumption and increase oxygen generation.

Heat reclamation

Devices are currently available that capture heat from residential and industrial greywater, through a process called drainwater heat recovery, greywater heat recovery, or hot water heat recycling. Rather than flowing directly into a water heating device, incoming cold water flows first through a heat exchanger where it is pre-warmed by heat from greywater flowing out from such activities as dishwashing, or showering. Typical household devices receiving greywater from a shower can recover up to 60% of the heat that would otherwise go to waste.