Grey water is defined as water from baths, showers, hand basins and clothes washing machines or the laundry.  Any water from any other source   ( toilet water,  kitchen and bidet’s) is considered black water, and must be allowed to proceed to the sewer, and be treated by some sort of sewerage treatment works.

Grey water is the biggest contributor to wastage of water and though knowledge of this very useful source is growing generally this knowledge is still woeful. In this form at best 33% of water consumed in the home is normally thrown away, and at worst is perhaps 50%.  It is preposterous that any municipality allows this precious source of good water to be thrown away.  Grey water is very useful for two purposes, re-used for toilet flushing or for irrigation purposes.

There are several rules for the re-use of grey water and the four most important are:

1. Thou shalt not store grey water:  This is the first law and may not be changed: the problem is that grey water has temperature and food value for anaerobic bacteria to breed and produce methane and hydrogen sulphide, the stuff that smells so badly.  Any talk of a “tank” into which grey water is fed and used for any purpose whatsoever is simply not possible. Any “tank” will build up sludge, and this is quite unacceptable.
2. Do not let grey water pool:  sending water to flood irrigate gardens on a regular basis means that a bacteria will clog the soil, preventing penetration of water into the soil, that needs to be overcome by some sort of cultivation
3. Grey water must be sprayed under very low pressure that does not exceed 6 metres head at the sprinkler.  This will prevent any atomizing of the sprayed water particles.  Grey water contains bacteria of many types, and the particles of water must land on the soil, and not float down wind to be breathed in downwind.  Spraying means that the likelihood of polluting groundwater is eliminated.  Grey water is dirty water and may not be fed into any irrigation system; this includes drip irrigation, because all irrigation systems require clean water and high pressure.
4. Perhaps the most important aspect to the re-use of grey water for irrigation purposes is what to use for washing powders.  The use of any phosphate rich washing powder will poison your soil over the long term.  There are phosphate free washing powders on the market, and these must be used.

If irrigated: moist soil teems with good bacteria, and will digest the food value of grey water in hours.  The byproduct of this digestion process is food (fertilizer) for plants to grow, and water.  That is your garden will grow fine without the need for any additional inorganic fertilizer whatsoever.

Grey water may also be used for toilet flushing purposes.  With this aspect the grey water is stored in multiples of small pump chambers (not tanks), and pumped directly into the toilet pan. The resultant saving is nearly as good as that of the re-use of grey water for irrigation purposes.