GREYWATER

If you are considering using wastewater from your home, there are environmental and health issues associated with this practice which can be managed. The following information outlines `best management practices' when using greywater. Domestic greywater is household wastewater, which has not come into contact with toilet waste. It includes wastewater from bathtubs, showers, bathroom wash basins, washing machines, laundry tubs and kitchen sinks.

ENVIRONMENTAL ISSUES

Greywater contains chemical pollutants that primarily come from household detergents and cleansers. Some chemicals present in greywater may be valuable fertiliser for lawn and garden watering. However, others may be harmful to vegetation and soils. These include sodium, total salts, chloride and boron. Untreated greywater from kitchen sinks, dishwashers and garbage disposal units should not be used for irrigation. Products can be chosen which contain none or reduced amounts of harmful chemicals. Water softeners and certain powdered detergents can contain sodium salts in high concentrations. Liquid laundry detergents generally contain lower concentrations of salts.

HEALTH ISSUES

While all greywater has the potential to cause disease, the danger varies considerably between households and between sources of greywater. For example, the risk of disease is generally lower in greywater from families without children compared with greywater from families with children. Laundry water from soiled nappies or wash water from domestic animals should not be used.

There is some evidence to suggest that background levels of disease causing organisms in the soil are often higher than from greywater used for irrigation. Greywater is also naturally purified by the biological activity in the topsoil.

HOW TO USE GREYWATER

The potential health risks associated with greywater irrigation depends on the source of the greywater and the way it is applied. For instance, if greywater is applied in the top 300 mm of soil through sub surface irrigation, disease causing organisms are less likely to survive than with surface application.

Greywater should not come into contact with the edible portion of fruit or vegetables. During long periods of dry weather, greywater irrigated areas should be irrigated periodically with normal or tank water to prevent salt building up in the soil.

Environment legislation requires that greywater reuse be kept within the boundary of the property from which it is produced. Overflows, including that from a greywater surge tank, must not be allowed to leave the property or enter the stormwater system. Avoid greywater use when the soil is wet or rain is imminent. Guide for permeable surface area required:


Storage of greywater promotes the generation of offensive odours and the growth of micro­organisms. Direct reuse is preferred. A surge tank may be installed between the plumbing fixtures sourcing the greywater and the reuse area on all greywater reuse systems. The surge tank should not contain a surge volume greater than 80 litres. An overflow drain should be provided at the top water level and should have a permanent connection to sewer.

PLUMBING AND DRAINAGE

Be aware of the likelihood of blockages in irrigation pipework caused by the accumulation of oils, grease and bacterial slime. This may be avoided by using pressurised systems. Household plumbing should be carried out by a licensed plumber in accordance with Australian Standards AS 3500 and AS 1345.