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06.Grey water for the garden

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 soil.

The GreySmart Household Product Assessment tool was developed using the framework of the Australian Guidelines for Water Recycling (2006). The hazards that were considered when grey water is used on household gardens are:

  • Acidity/alkalinity or pH – laundry detergents are highly alkaline (that is, have a high pH) to help dissolve organic dirt, such as grease, oils and food scraps. Most biological systems prefer a pH between 6 and 9, and grey water with a high pH is likely to harm many plants and soil organisms.
  • Total alkalinity Laundry detergents contain chemical "buffers" to help prevent pH changes in the water/detergent solution, thereby maintaining optimal pH level. A measure of total alkalinity tells us that many are very highly buffered, so would require enormous amounts of acid to counter the alkalinity. If you put this water onto soil, the pH of the soil would be more likely to change than that of the grey water.
  • Electrical conductivity or salinity – a measure of the dissolved salt content of water
  • Boron – present in some laundry detergents to reduce water hardness and aid bleaching. Boron is an important plant nutrient, though it can be a problem if there’s too much. The small amounts of boron in laundry water shouldn’t cause any problems unless the soil is prone to water logging for long periods.
  • Cadmium – a contaminant in some components of powder laundry detergents
  • Phosphorus – small amounts of phosphorus can be useful for plants, and it’s a major component of fertiliser. Australian soils are typically low in phosphorus, and some native species can’t tolerate high levels. Higher levels of phosphorus can be acceptable if you have clay soil, because it binds to clay minerals and doesn’t leach away. On sandy soils, excess phosphorus can leach into groundwater. When it gets into waterways it can contribute to excessive algal growth, leading to toxic algal blooms.
  • Nitrogen – present in many solid and liquid laundry detergents.
  • Sodium adsorption ratio - a ratio of the sodium (detrimental element) to calcium and magnesium (beneficial elements) and is related to known effects on soil surface structure and soil stability. All laundry detergents contain sodium salts, typically sodium nitrate, sodium sulphate, sodium phosphate and sodium silicate. Table salt – sodium chloride – isn’t used in detergents.
  • Residual sodium carbonate – calculated using milli-equivalents of calcium, magnesium, carbonates, and bicarbonates and combined with Sodium Adsorption Ratio to evaluate impact of carbonates on the sodium hazard in water applied directly to the soil.
  • Degradability of organic chemicals – there are many organic chemicals in both powder and laundry detergents.

For a summary of the ranking system criteria, see

Claims on packaging

Some products are marketed as "green" detergents. Presumably, we’re meant to think their impact on the environment is less than that of regular laundry products. In reality, all detergents, no matter what's in them, affect the sewerage system and aquatic environment.

A laundry detergent is a complex product made up from numerous chemicals. To determine its full environmental impact, you’d need to assess the physical, biological and chemical effects of its formulation on the environment.


This is the ability of chemicals to break down naturally in the environment. Manufacturers tend to make claims about biodegradability in reference to the Australian Standard. All laundry detergents must comply with this standard anyway, though it’s limited. It states that 80% of the surfactant must break down within 21 days. There’s no mention of the other 20%, or of chemicals produced during the breakdown process which could be toxic or non-biodegradable. Furthermore, there are many more ingredients in a detergent - it's not just surfactant, and there's no regulation on these.

More about grey water

What’s your soil?

If you don’t know what type of soil you have, this quick test will give you an idea. Take a handful of soil, add a little water and make it into a ball.

  • Loam soil will form a moist ball with an "earthy" smell. It’s usually brown, and holds and drains water well.
  • Clay soil forms a hard, smooth ball. Its fine, dense particles inhibit water movement, and when it dries it resists water. Its colour can range from white to red to dark brown.
  • Sandy soil is soft and crumbles easily – it probably won’t form a good ball. It’s light in colour, has little or no smell and is low in nutrients and organic matter.

Using grey water

  • Grey water can be treated and stored and used on the garden (or even in toilets or washing machines), or else it can be diverted 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 usage to water from the shower or bath, and the rinse water from the washing machine. Kitchen water contains fats and solids that might damage soil and plants.
  • Don’t store untreated grey water for more than 24 hours; if you can’t use it, don’t keep it.
  • If someone in your family is sick with gastro or flu or another contagious disease, stop using the grey water.
  • Don’t water herbs or vegetables.
  • Don’t water pot plants.
  • Keep the grey water underground, or under mulch – this helps prevent evaporation, as well as keeps it away from kids and pets.
  • We tested only the wash water for chemicals that could harm your garden. What comes out of your machine may also include dirt, bacteria and viruses from the dirty clothes. These are good reasons for not storing untreated water from your washing machine.
  • Potential impacts are very much dose-dependent – try reducing the amount of detergent you use.

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