There are a number of factors to look for in a grey water system that will help in determining whether the system is correctly designed to provide safe use and ease of maintenance. The following general rules will help when you look for a grey water system:

Size of chamber:

This is where your wastewater is temporarily stored before being pumped to garden. The chamber should be as small as possible, around 50 – 100 litres. The idea is to pump out your grey water as soon as possible. Larger systems that store grey water build up anaerobic bacteria within a couple of hours resulting in associated foul smells. It is these ‘storage’ type systems that give grey water a bad name.

Type of pump:

Your pump should be low pressure. High pressure pumps atomise (mist) grey water resulting in harmful pathogens floating in the air that can be breathed in. A good system will have a low-pressure submersible pump inside the chamber that is virtually silent when on. External irrigation pumps should be avoided at all cost.

Irrigation:

Grey water is to be dispersed to the garden using either drip pipe or a pyramid type sprayer where larger water particles – delivered by a low-pressure pump – fall to the ground. Grey water should never be pumped through a standard irrigation system that requires pressure to drive the sprayers. High pressure pumps atomise (mist) grey water resulting in harmful pathogens floating in the air that can be breathed in.

Filtration:

The better systems will have a filter basket (much like a pool filter basket) for larger particles and a membrane (type of carbon sponge) for smaller particles. In the case of drip irrigation, a further in-line filter is required so that the fine holes in the drip pipe do not become clogged.

Cleaning the system:

To avoid a smelly grey water system the filters should be washed weekly and the main chamber cleaned every 6-months. The membrane filter should also be replaced 6-monthly. For this reason, easy access to your system is important.

Detergents:

Another factor to look for is if the supplier can provide washing powder and cleaning detergent that are developed with the correct enzymes to digest nutrients and particles in the water. Use of the correct washing powders and cleaning detergents will help mitigate smells by reducing the build-up of anaerobic bacteria in the waste pipes and chamber.

There are distinctly 2-types of grey water systems; those that do not treat grey water and those that do treat grey water.

a) Systems that do not treat grey water are used for garden irrigation only. These are diversion systems where wastewater from baths, showers, basins (not kitchen sink) and washing machines is diverted to a partially submerged chamber. From here it is pumped to the garden automatically to either drip pipe or low-pressure sprayers. The filtration used in these systems is normally a basket type filter to remove larger particles.

b) Systems that do treat grey water are used for flushing toilets, laundry washing, pool top-up and garden irrigation. The treatment used in these systems would include digestion (of the grey water bacteria) and either UV-sterilisation or membrane filtration. Although these systems are more versatile the cost is usually far greater than the simple diversion system for garden irrigation. See Hydraloop and Aqualoop treatment systems.