Sources, Installation and Uses of Grey Water
Wastewater is categorised as either grey water or black water
Grey water is made up of the wastewater from our showers, baths, spas, hand basins, laundry tubs, washing machines, dishwashers and kitchen sinks. (It doesn't include water from toilets.) Used appropriately, you can water your garden with grey water and save around 400 litres of fresh water each day.
Grey water can be diverted to your garden through direct diversion or a domestic grey water treatment system (DGTS). A DGTS will produce higher quality grey water to use in the garden and possibly your toilet or washing machine.
Black water is made up of the wastewater from our toilets, urinals and bidets. It is grossly contaminated by human excrement and requires a detailed treatment process such as a composting toilet before it is suitable to use in the garden.
How much wastewater do households produce?
The amount of wastewater generated by any household varies greatly according to the number of people, their age and lifestyle. For instance, in Sydney an average household (3.5 people) produces 586 litres of wastewater each day.
Approximately 61 per cent of the total wastewater produced by an average household can be used as grey water. Kitchen wastewater is not usually included in this amount.
Things to consider
• Untreated grey water is best diverted from the bath, shower and laundry rinse cycle only.
• Using untreated grey water in your garden means you may need to cut back on the amount of fertiliser you use.
• Treated grey water has had most nutrients like nitrogen and phosphorus removed, so it's safer to use in large quantities.
• Only use grey water with watering systems that are under the soil surface.
• Avoid using grey water on vegetable gardens if you're going to eat the vegetables raw or lightly cooked.
The following grey water procedures should be implemented.
1. Ensure greywater does not contaminate any source of drinking water: extreme care must be taken to ensure there is no cross-connection between the greywater reuse system and the drinking water supply.
2. Ensure that the diversion system is fail-safe, that is, grey water will automatically be diverted to the sewer if the greywater system blocks or otherwise malfunctions.
3. Direct greywater to sewer during periods of wet weather.
4. Do not divert kitchen wastewater, which has a high concentration of contaminants not readily broken down by soil organisms.
5. Only divert the lowest risk greywater, such as the shower, bath, hand basin and laundry rinse water.
6. Never divert greywater that could have gross faecal contamination, for example water used to wash soiled nappies.
7. Apply greywater to the garden by sub-surface irrigation.
8. Always wash your hands after gardening.
9. Do not irrigate vegetable gardens supplying food crops that are eaten raw or undercooked
10. Never store untreated greywater for more than 24 hours.
11. Do not allow greywater to pool or stagnate as this will attract insects and rodents
12. Never allow greywater to discharge beyond property boundaries, as this may create environmental and public health risks.
13. Never allow greywater to discharge to a drain or waterway
14. Never drink greywater or allow pets or animals to drink or have access to it.
15. Use low phosphorus detergents.
16. Reduce fertiliser use when irrigating with greywater.
17. Do not allow the soil to become saturated. Carefully monitor the impact of the greywater on the irrigation area in order to minimise the risk of causing pollution.
Source: Reuse Options for Household Wastewater, EPA Information Bulletin, Publication 812, Domestic Wastewater Management Series, November 2001
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