Grey water recycling

Greywater is waste water from showers, baths, washbasins, washing machines and kitchen sinks. You can collect it from some or all of these sources and, after treatment, use around the home for purposes that do not require drinking water quality such as toilet flushing or garden watering. However, water from kitchen sinks and washing machines tend to be more contaminated than shower etc and so should not be used as a source of grey water unless you are thinking about a more complex treatment system.

The final use of the recycled water is really important to consider. If you have low flush toilets, no garden, or are the type of family that rarely washes the car, then looking at new grey water recycling systems should be a low priority.

The pie chart below sets out average use for the UK. The only segment that shines out for grey water use is the toilet flushing. Given that water use can be radically reduced (around 50%) by using equipment like Interflush or Mecon variable flushes the figures that you can affect by recycling water are quite minimal.

Currently there are no regulations to cover the quality of reused water. Although there are some national standards relating to reused water that have been developed by the British Standard Institute and these would require a system that has:

• a tank for storing the treated water;
• a pump;
• a distribution system for transporting the treated water to where it is needed; and
• some sort of treatment.

So if you are to store the water then a more complex (and hence expensive) system is required. This is because untreated greywater deteriorates rapidly in storage.This rapid deterioration occurs because greywater is often warm and rich in organic matter such as skin particles, hair, soap and detergents. This warm, nutrient-rich water provides ideal conditions for bacteria to multiply, resulting in odour problems and poor water quality. Greywater may also contain harmful bacteria, which could present a health risk without adequate water treatment or with inappropriate use. The risk of inappropriate use is higher where children have access to the water.

Do not worry, though, as it is possible to reuse greywater without any treatment provided that the water is not stored for long before use. For example, once bath water has cooled, it can be used directly to water the garden. Very simple devices are available to make this practical. Among these is the ‘WaterGreen’ by Droughtbuster UK Ltd , which is essentially a hose pipe with a small hand pump to create a siphon. This allows cooled bath water to be taken directly from the bath and sent through the hose to the garden. Using greywater in this way may not suit everyone, but it does provide an inexpensive and easy way of saving water and avoids greywater storage issues. It is particularly useful for keen gardeners when water use restrictions are in place. Experts usually advise that greywater should not be used on fruit or vegetable crops.

Other equipment is designed to reuse greywater direct from a sealed main drainage system. For example, a valve can be fitted to an external waste pipe that drains water from the bath or shower. This valve can be used to direct greywater to a water butt where, once cooled, it can be used for garden irrigation. An example of this type of valve is the ‘Water Two’ valve, which can be fitted to existing piping and switched to either divert greywater to a drain or to storage.

Our advice therefore would be to think about water use and to reduce consumption as the first course of action. Once this has been minimised, then you can re-assess what your demands are and then see if grey water use is right for you. Note that rain water harvesting and use might be a better option than grey water use.

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