08 March 2011

Greywater keeps it green

It's possible to save water during the dry months without having to watch your beloved garden shrivel. Greywater doesn’t sound appealing, but it helps keep things green.


It's possible to save water in summer without having to watch your beloved garden shrivel in the heat. Greywater doesn’t sound appealing, but it helps keep things green.

What is greywater?
Greywater, sometimes known by the equally unromantic name of ‘sullage’, is used water that contains some impurities but isn’t heavily polluted. As you might expect, it's no longer suitable for drinking, but it still has plenty of use left in it.

Household greywater includes water that you’ve used to wash yourself (i.e. from the bath, shower or basin), or do the laundry.

Re-using greywater significantly reduces the amount of fresh water needed for your household, and also the amount of waste water entering the sewerage system.

Great for the garden
Greywater can be safely re-used to irrigate plants, so don’t hesitate to use it on your garden. It contains low concentrations of soap, which actually suits most garden plants.

The contaminants in greywater break down quickly when exposed to the elements, and the plant roots and soil organisms in your garden speed up this process.

The following tips can help make ‘greywatering’ safe and effective:

  • For the most part, gardens thrive on greywater, but it’s still a good idea to switch to fresh water every now and then – say once a week.
  • Apply greywater directly to the soil, i.e. at ground level and not via a sprinkler, to minimise its contact with foliage.
  • Don’t use greywater on root vegetables (like carrots) which will be eaten raw.
  • Greywater is alkaline, so don’t use it on plants that prefer acid soil.
  • Use greywater on established plants, not seedlings.
  • Spread greywater over a wide area – don’t always use it on the same section of your garden.
  • Some greywater is only suitable for toilet flushing, not irrigation. This includes water containing fabric softener, water from washing dirty nappies and water from washing clothes heavily soiled with petrol or industrial pollutants.
  • Don’t re-use dishwater. It's also sometimes included in the definition of ‘greywater’, but it's not suitable for recycling in this way. It contains chemicals that might damage plants, and food residues that can cause unwanted bacterial growth.
  • Try to use greywater within 24 hours, or the rising bacteria count will start to cause odour. You can keep it a few days longer, but then you’ll need to treat it by adding about half a tablespoon of bleach per litre – and that, of course, adds to the chemical load.
  • Don’t let children or pets play with or drink greywater.
  • Improve the quality of your greywater at source by using less soap, cosmetics and laundry detergent.

Other ways to go grey
In addition to re-using greywater in the garden, you can also use it to flush the toilet. Every time you do, you save about 12 litres* of fresh water – the amount used for a regular flush mechanism.

Again, don’t go grey exclusively. Use the regular flush mechanism once a day – and certainly for faecal matter. Remember the timeless maxim:

When it’s yellow, let it mellow,
When it’s brown, flush it down!

Only put greywater into the toilet bowl, not the tank, as it can damage the flushing mechanism.

You can also use greywater for sluicing down paved surfaces outdoors – but make sure it doesn’t run into your neighbour’s property or the street.

What about greywater systems?
If you want to go grey, but don’t fancy lugging buckets of bathwater around, you may want to consider having a greywater system installed.

There are several on the market. Some involve fairly simple mechanisms to re-rout greywater from outflow pipes to your garden, and others treat the water as well. The latter are controversial, because it’s doubtful whether the cost (financially and environmentally) of installation and upkeep justifies the savings you make in the long run.

*Stat from the Department of Water Affairs and Forestry

- Olivia Rose-Innes, EnviroHealth, Health24, November 2006

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