Grey water for the garden
Grey water is the waste water from showers, baths, spas, hand basins, laundry tubs and washing machines. With water restrictions operating in many parts of Australia, using grey water on your garden could save hundreds of litres of water per day. But it shouldn't be used on herbs and vegetables.
Grey water can be treated (for example, filtered and treated with micro-organisms or chemicals) and stored to be used on the garden, or even in your toilet or washing machine. Alternatively it can be diverted directly to the garden with a plumbed-in diverter (with a switch so that if it’s raining, it goes into the sewer instead). Conditions may apply in the area where you live — contact your local council for advice on options available.
If it’s untreated, limit your usage to water from the shower or bath, and only the rinse water from the washing machine. Take a look out our laundry detergent test to see if your greywater is suitable for reuse in the garden www.choice.com.au/detergents . Kitchen water contains fats and solids that might damage soil and plants. DIY options include attaching an extra-long flexible hose from the washing machine to the garden, or using a bucket.
Don’t store untreated grey water for more than 24 hours. If you can’t use it (because it’s raining, say) don’t keep it. If you’re treating and storing it, keep the grey water underground, or under mulch — this helps prevent evaporation, as well as keeping it away from kids and pets. Grey water should not be used at all if someone in your family is sick with gastro or flu or another contagious disease.
Washing machines account for almost a quarter of household wastewater or — depending on your machine — about 60 to 180 litres per wash.
We tested the wash and rinse water for chemicals that could harm your garden. What comes out of a washing machine will also include dirt, and perhaps bacteria and viruses from the dirty clothes. These are all good reasons for not storing untreated water.
Please note: this information was current as of October 2009 but is still a useful guide to today's market.
Use rinse water
Thanks to the effective removal of excess detergent during the post-wash spin cycle, rinse water is almost clean water. A switch on your plumbed-in diverter will allow you to use only rinse water, but unless you have an automated system, you’ll have to keep an eye on the cycle and activate the switch between the wash and rinse cycles.
The switch will also let you pump grey water into the sewer if it’s been raining (so is not needed on the garden). It also makes it easy to avoid using the water if you’ve been washing nappies, someone’s been sick, or you’ve used bleach products in the wash.
The larger the irrigation area, the more you’ll spread the chemical load. Our recommendations are based on an irrigation area of 150 to 200 square metres. Don’t use it to water pot plants.
Accumulated chemical load
If you collect the wash and rinse water before using it, the contaminants in the wash water will be diluted. However, the criteria we used in our chemical testing considered the total load of problem chemicals that will accumulate in your garden over time, not just their concentration when you first put them on, so the recommended irrigation area (150 to 200 square metres) still applies.
Potential impacts on your garden are very dose-dependent — you could try reducing the amount of detergent you use, providing it still gets your clothes acceptably clean.
There have been reports of grey water hoses acting as a siphon and pumping water from the washing machine while it’s still washing or rinsing — something to consider if your washing machine doesn’t seem to perform as well as usual.
The water from washing machines contains several chemicals that aren’t good for plants or soil. If the concentration or total load of these chemicals is too high, you’ll eventually end up harming your plants and wrecking the soil.
CHOICE arranged for a lab that specialises in soil, water and wastewater analysis to test the wash and rinse water from all the liquid detergents at the concentrations recommended by manufacturers for front and/or top-loader machines, as appropriate.
The components most likely to cause problems are:
We also looked at sulphur, boron and total alkalinity.
Results were considered on a per-wash basis, assuming intermittent use only in your garden (interspersed with clean water) and over an area of no less than 150 to 200 square metres.
The rinse water for all detergents was found to be acceptable. The wash water for those with a tick in the 'OK for the garden’ column of the results table meet all the criteria for safe use if used as above. Note that the amounts used were those recommended for 'normally' dirty clothes — if you use more detergent the results will be different. The less detergent the better for grey water reuse.
Choice's Green Watch campaign found a detergent that's claiming to be safe for greywater use, when it isn't. Listen to our podcast below and go to www.choice.com.au/campaigns
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