Why Use Grey Water?


 grey water recycling


What is Grey Water?

Grey water is untreated used water from washing machines, bathtubs, showers, and bathroom sinks. Wastewater from a kitchen is also called grey water, but it is separated because of grease and oil contamination. Kitchen greywater should undergo treatment before discharging into the environment and it should be directed to a sewage system.

Wastewater from toilets and commercial wastewater is called black water or sewage.


Why Recycling Grey Water

The clean water supply is decreasing for many reasons and about half of the global population does not have access to clean water. Saving water has become a part of the response to environmental issues and reusing greywater can help reduce water consumption.

We use an average of 200 Liters of water every day per person in Australia. In the USA, the average consumption is about 300 Liters. On top of this, garden turf needs 10 Liters per square meter, for washing cars, pools, etc. By reusing grey water from the washing machine alone, we could save 300 to 700 Liters per week.


Where Can Grey Water Be Used?

Generally, grey water can be stored and used to flush toilets or water the garden. But rules can be slightly different depending on the local regulation.

There are some safety tips you need to keep in mind:

  • You should use grey water within 24 hours. If you cannot use it, do not keep it. Do not store it.
  • If you are filling up buckets, do not leave the filled buckets where little children can reach.
  • You could install a treatment system. If you don’t have a system, recycle only the rinse water from a washing machine.
  • Fats and solids in kitchen wastewater could damage plants
  • Grey water is fine for irrigating fruit trees or landscaping plants but does not use directly on edible crops.
  • Never rely solely on grey water to water your garden. Build-ups in the soil can harm your garden.
  • Try to spread grey water around. Don’t always dump it in the same spot.
  • A subsurface irrigation pipe system is the lowest risk for using grey water outdoors. Hosing it onto the surface of the soil is considered a high-risk option.



Are Cleansers And Personal Care Products in Grey Water Safe?

laundry detergent

Any untreated wastewater should not be discharged into a stormwater drain or natural water source. Organic matters in grey water become pollutants in aquatic ecosystems, but they are valuable fertilizer to the soil. Not all organic matters are good, and there are a few rules.

  • Salts such as sodium nitrate, sodium sulphate, and sodium phosphate often contained in cleaning products are harmful to both plants and soils.
  • Alkaline pH, higher than pH 8 for liquid cleansers or 10 for powders, will likely harm many plants and soil microbes.
  • Phosphorus can be useful for plants in a small amount, but it can cause excessive algae growth when it gets into waterways.

Therefore, all-natural doesn’t mean safe for grey water. Soaps including castile soap are highly alkaline, around pH 9.3. Other common ingredients for natural laundry powder and bath products such as baking soda and sodium salts can be harmful depending on the concentration.

The product package may indicate if it is safe for grey water. If you are not sure about the ingredients in products, only recycle rinse water from a washing machine.




Greywater - https://en.wikipedia.org/wiki/Greywater

Greywater and sewage in the Environmental Protection Act - https://environment.des.qld.gov.au/__data/assets/pdf_file/0038/88976/pr-is-greywater-sewage-acts.pdf

Grey Water - https://www.burkesbackyard.com.au/fact-sheets/conservation-the-environment/grey-water/


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