Water Talk Part II

Grey water is probably better described as 'used water' such as the water from wash basins, baths or showers. Although not clean enough for consumption or food preparation, with proper treatment greywater can be put to good use. Typically there are only two ways to dispose of water from your household, the first being the stormwater system (for which greywater is not clean enough to be disposed into) or into the sewerage system (for which greywater is not dirty enough for). Reusing greywater requires a bit more thought and investment in the initial setup than setting up a rain water harvesting system, however by using greywater for watering gardens and lawns, a household has the potential to save between 50,000 and 100,000 litres of drinking water a year![1]

As was outlined in ‘Water Talk Part I’, the majority of our water uses don’t require clean drinking water to be wasted on things such as toilet flushing, showering or watering the garden. The first step to reducing this waste of clean drinking water is to install a rain water harvesting system, however if this isn’t collecting sufficient water for your needs or if you want to further recycle and reuse harvested water; a greywater re-use system may be a good solution.

There are two ways in which greywater can be reused. The first is without treatment. Untreated greywater can only be used outdoors to irrigate gardens and lawns (but not food producing plants) and should be used within 24 hours as bacteria and pathogens may be present in the water, however the nutrients in the greywater such as phosphorus and nitrogen provide an excellent food source for plants[2]. The second way to reuse greywater is with a treatment system, which in NSW is the only way in which greywater is allowed to be used indoors (e.g. toilet flushing, washing machine).

Greywater sources for untreated greywater systems. Source: Standards Australia and the National Water Commission

Greywater systems can be either a gravity-fed or pumped setup. A gravity-fed setup relies on using gravity to irrigate a garden or lawn that is at a level lower than the source of the water. However, the slope of your site or if you need to pump to a toilet or washing machine, you may need a pumped setup. If you are using a treatment system, there are a variety of treatment methods including filtration (to collect lint and hair), micro-organism or chemical treatment and in some cases disinfection by chlorination or UV light.

It is also possible to treat grey water naturally with the use of a ‘reedbed system’ which uses natural processes to treat the water. Water trickling through the reed bed is cleaned by microorganisms living on the root system and in the litter. A reedbed system also need a lot of thought up front to ensure that they operate effectively.

Diagram of a typical domestic greywater reedbed system

Because of the potential health risks of greywater, time should be taken to consider the most appropriate method of treatment (dependent on the intended use) as well as the setup of the system itself to ensure that maintenance and use are as user-friendly as possible. To find out more about greywater systems you can download this detailed guidebook from the NSW Office of Water or speak to an architect.

[1] http://www.water.nsw.gov.au/urban-water/recycling-water/greywater
[2] http://www.sustainable.com.au/greywater-treatment.html