Issue 8, October 2003

Good quality drinking water in many areas is becoming a scarce commodity. Additional demands will be placed on limited water supplies as populations increase with perhaps little scope to expand water supply catchments. Greywater is just one method that provides an opportunity to conserve water usage.

Greywater is wastewater typically considered to be from a hand basin, bath/shower, or laundry. Kitchen wastewater is generally unsuitable without some form of treatment. In domestic premises greywater represents about 61% of wastewater.

Greywater can be contaminated from:

• Micro-organisms many of which may be pathogenic;
• Chemical pollutants such as dissolved salts of sodium, nitrogen, phosphates and chlorides, or by chemicals such as oils, fats, soaps and detergents, which may provide food for micro-organism and plant growth;
• Physically polluted by particles of dirt, food, lint etc.

Untreated greywater is best diverted from the bath, shower and laundry rinse cycle only. Storage of untreated greywater should not be stored longer than 24 hours, if at all, as it will turn septic giving rise to offensive odours and provide conditions from micro-organisms to multiply.

When using greywater in your garden you may need to reduce the amount of fertiliser used. Greywater should be applied only by watering systems that are under the soil surface. Avoid using greywater on vegetable gardens if you are going to eat the vegetables raw or lightly cooked.

Greywater can be classified based on treatment and use restricted to particular situations; e.g.:

• Coarsely filtered untreated greywater (excluding kitchen greywater) for sub-soil or sub-surface irrigation.
• Treated and disinfected greywater (20 mg/L BOD₅, 30 mg/L SS and 30 cfu thermotolerant coliforms /100 mL) for sub-soil irrigation, sub-surface irrigation and surface irrigation.

The consideration to use greywater should be done with an awareness of the health risks and environmental degradation that may be caused. To use greywater sensibly it is necessary to install suitable equipment and land application systems that protect public health and are ecologically sustainable. 

There should be no general approach to installing a greywater system on your property.  Each system should be designed on a case by case basis.

CETEC can assist you with your projects, including conserving water within your business facility.  For more information or a review of your facility about Water Harvesting and reducing your Water Usage call us NOW on 03 95449111.

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