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GREYWATER REUSE
Society is becoming more water concious due to shortage, population growth and drought. At the same time, there is concern about the impact and waste of sewage and effluent disposed from sewage treatment plants into our ocean, and other environments. Greywater accounts for approximately 40% of all water used in domestic dwellings in Australia, and 70% of the total wastewater volume. In Sydney alone wastewater volume discharged into the ocean yearly is quoted as 500,000 Megalitres/yr (eg. the same volume as Greater Sydney Harbour). 70% of Sydney Harbour would be quite a good saving. Greywater reuse for garden irrigation to both conserve water and to reduce ocean discharge makes good sence.

Historically, 'greywater' (by legal definition) was considered by regulators to be no different from sewage (ie. 'sewage' being all wastewater including greywater and toilet waste). Under that historic yet simplistic definition greywater reuse was caught up in the same public health and environmental impact risk control regulatory frameworks necessary to stop disease spread and control pollution from poorly designed sewage treatment and disposal systems. This previously meant domestic greywater diversion was either not permitted when sewer was available or when it was permitted it could only occur through onerous onsite sewage regulatory frameworks and local government approval processes that detered all but the most tenacious householders doing it by legal means. In reality what this meant was that many householders simply did it outside the law to avoid the bother of going through the complex red tape legal channels.

Today with the focus on the need for water conservation the risks associated with domestic greywater diversion for the garden are rapidly being put into their proper perspective. It is recognized that pulling a plug from your kids bath or the laundry trough to remove a blockage is not the same risk as inserting a hand into a septic tank or a sewer and likewise it is already known that septic tanks had successfully disposed of all 'sewage' (including the 'greywater') for decades from houses without significant pollution.

Consequently in most Australian states today the red tape regulatory frameworks that previously handicapped domestic greywater diversion is slowly being removed. NSW is the leading state in regard to the removal of that red-tape with the release of their "NSW Guidelines For Greywater Reuse in Households 2007 ". See the NSW Department of Energy, Utilities and Sustainability website for further info.

WHY IRRIGATE WITH GREYWATER
Greywater comes from the bathroom, laundry and kitchen. Whilst greywater does not contain toilet waste it nevertheless generally contains the same pathogenic micro-organisms (though in much lower numbers) just from washing your hands, bathing and washing soiled clothing. Therefore, health authorities recommend caution when reusing greywater. The best means of addressing their concerns, without use of expensive and often un-reliable treatment and disinfection technologies is simply to irrigate greywater below the ground surface to avoid un-necessary human contact.

Whilst greywater will always contain some micro-organisms the health hazards from a multi dwellintg greywater source are significantly greater than from a single dwelling greywater source. This is beacause within a single dwelling setting inhabitants already have intimate exposure to the same greywater whilst bathing and washing and essentially to their existing family unit's reservoir of micro-organisms, whereas exposure to greywater from multi dwelling sources has potential to expose an individual to micro-organisms not already present within their family unit and there a greater potential for spread of disease.

Greywater contains traces of oils, fats, detergents, soaps, nutrients, salt and particles of food hair and lint etc, that can quickly clog a greywater subsurface irrigation system. Whilst greywater from the kitchen contributes least to the total greywater volume it accounts for the bulk of fats, oils and food particles, which are the primary components that cause this cloging. In contrast, greywater from the bathroom and laundry account for the majority of the greywater stream but generally contribute little of the components that cause clogging and therefore generally requires only removal of suspended particles such as lint and hair. For this reason most states only consider greywater from the laundry and bathroom as suitable for diversion for irrigation.

GREYWATER AND PLANTS
Greywater contains contaminants, which vary in their effect from beneficial to detrimental for irrigation of plants. These contaminants include nitrogen, phosphorous and potassium, which in most cases are beneficial to plants, except for a small number of native plants that have a unique low phosphorous or nutrient tolerance from having evolved and developed in marginal nutrient depleted soils. Greywater also generally has a slightly alkaline pH making it preferable not to use greywater to irrigate acid loving plants, unless the pH is managed, by digging soil conditioners such as peat or compost into the soil. Suitable plants and soil conditioners should be discussed with your local gardening centre.

Some laundry detergents and bleach will results in greywater with increased levels of sodium salts that can be detrimental to plant growth. Therefore, it is preferable to use products with low sodium levels, as found in most but not all liquid laundry detergents. Some strong household products such as caustic soda (drain cleaner) can be detrimental to plant growth and when used the greywater should be diverted to the sewer or septic tank.

When greywater is being reused for garden irrigation users simply need to think about what is being sent to the garden via their greywater system and to not use excessive amounts of household cleaners and detergents so as to minimise any impact on plants and simply because overuse is wastefull.

MORE INFORMATION
For further information about greywater gardening and garden friendly greywater products search the Web.