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What is Greywater and Blackwater?

Types of Wastewater - Greywater and Blackwater

Every day the water we use in our household ends up becoming wastewater. The wastewater, depending on where it was used, and any chemicals in it end up either as blackwater or greywater. For example, the water used in the toilet is heavily contaminated and classified as blackwater, whereas the water used to wash your hands has a low level of contaminants so it is deemed greywater. The wastewater can be reused and treated with biological and chemical methods for recycling.

What is Blackwater?

Blackwater is the wastewater from toilets or urinals which consists of urine and faecal matter. Water from kitchens and dishwashers can also be classified as blackwater due to the presence of pathogens and grease.

Blackwater has a higher level of organic matter compared to greywater and is a hotspot for disease-carrying pathogens. This type of wastewater is unfit for human and animal consumption and blackwater must not be used for household purposes or recycled as it cannot break down effectively in on-site treatment plants without the risk of contamination.

How is blackwater treated?

Blackwater can be treated by biological and chemical methods using on-site sewerage facilities like:

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What is Greywater?

Greywater is the water from non-toilet plumbing fixtures like taps and showers.

A large volume of greywater comes from household activities like dishwashing, laundry, and showers. There are organic pathogens, bacteria and chemicals present in grey wastewater but it can usually still be recycled for household purposes. Greywater hasn't come in contact with faecal waste so it is unlikely to contain disease-carrying pathogens and can be broken down safely during treatment and in gardens and lawns. The chemicals and organic matter present in the greywater can be absorbed by worms, plants and microbes in the soil. It can also be treated and used to flush the toilet and in the laundry.

How is greywater treated?

Biological treatment methods like sand filters and coarse filtration techniques can be used to treat greywater.

Both greywater and blackwater are not suitable for consumption.

If you are planning to reuse greywater in your home, make sure there are separate channels for greywater and blackwater. This will prevent the contamination of greywater and also help you reuse water safely. It helps to minimise the use of chemicals in your home and regulate what you flush down the drain.

What is Greywater or Blackwater Infographic

Benefits of Reusing Greywater

  • Conserves water
  • Irrigates the garden using minimum resources
  • Reduces water bills
  • Puts less strain on the municipal infrastructure for treatment, and disposal

How to improve the wastewater quality in your home?

  • Minimise the use of cleaning chemicals
  • Use natural and non-toxic products
  • Use a sink strainer in the kitchen to prevent food debris from entering your wastewater
  • Avoid using soaps, body wash and detergents with high sodium
  • Clean and replace the lint filter in your washing machine regularly