Grey Water Systems


This is something extremely useful in helping reduce the amount of potable drinking water from our limited supply in dams and replacing this water used for irrigation with grey water.

Grey water is the water which comes from sinks in the bath and laundry. They have soap, fibers and other debris, but no human faeces. This water can be filtered, purified and reused for garden irrigation after passing through a simple-to-build biological filter.

Bio-remediation is an increasingly popular method for water treatment. Some aquatic plants even are used to remove nutrients and reduce the concentration of phosphorus and nitrogen from raw sewage or wastewater treatment facilities. Aquatic plants are also capable of absorbing heavy substances, including pollutants.

A strategy like this is very useful, especially in arid or drought periods so as not to let the plants die of thirst.

If you want to get started, try first reusing the grey water of the washing machine directly in the garden. This water has few substances such as pathogens and unwanted fat. But low-sodium soap such as sodium harms plants and degrades the soil to be sure to check that your detergent doesn’t contain this.

To create a system for recycling grey water is not complicated: a series of tanks are built to act as a sequence of filters. As the water passes through the tanks it is gradually purified by biological action of micro-organisms and the plants introduced there.

This treatment simulates natural systems where a combination of micro-organisms and plants plays the role of ‘filtering’ the effluent.

First, remember to check all the possibilities of reducing your water consumption before deciding on the treatment system for grey water.

Many people use wastewater from the kitchen sink also, but this must pass through a grease trap (pre-treatment) before entering the bio-remediation system. In Australia there are some laws preventing water use from the kitchen sink, so check with your local Council as to what they recommend.

To make the system filter even more efficiently, you can introduce a layer of ash (rice hulls, oat or wheat burned).

After passing through a series of tanks containing an impermeable porous substrate (sand, gravel and stones) and plants adapted to waterlogged soils. This serves as a preliminary filter for larger particles.

If you find live mussels, put them in the last tank. These animals make excellent filtration of water and are a good indicator of how the system is operating. Place fish and enjoy the beauty of the floating plants. Now the water is again clean and ready to irrigate the orchard.

Plants perform an important task in intermediate tanks. Absorb the “pollution” dissolved in the water turning it into biomass and releasing of the water in vapor form.

Their roots digest a lot of waste found in the gray water. In addition, harbour bacteria and other micro organisms that make the digestion of nutrients and clean water.

Thus, excess minerals, as well as some human pathogens, are removed, making the water safe for reuse in irrigation of the soil.

Plants used in water purification systems:
Common Name/Scientific Name
Water lettuce/Pistia stratiotes
Azola/Azolla caroliniana
Camalote/Pontederia rotundifolia
Marsh grass lake/Schoenoplectus
Maltese cross/Ludwigia sedoides
Iris/Iris pseudacorus
Common reed/Phragmites australis
Gecko/Sagittaria guayanensis
Ear-of-oz/Salvinia auriculata
Papyrus/Cyperus papyrus
Cattail/Typha latifolia
The yellow and green microscopic algae to convert solar energy into complex molecules, which can be passed to others in the food chain. The same principles apply to forests, fields and oceans. The micro organisms create the basis for life on planet Earth; they are supporting humans and all other living things.

Basic rules for use of grey water:

  • Give priority to the use of clean grey water.
  • Always check the flow of the system. The grey water shall not be stored or displayed, as it can cause odour. If stored for a long time it can create pathogens.
  • Do not use sprinklers to irrigate with recycled grey water, because that way the water can accumulate around the house and leave an unpleasant odour. It is best to irrigate by gravity, allowing water to penetrate the soil.
  • Make a rotation of the irrigation areas with grey water, avoiding the accumulation of salts in the soil.
  • Check out the soap you are using. Give preference to those who have no boron and avoid bleach (chlorine). Choose non-toxic soap.
  • Use liquid detergent instead of soap powder.
  • Avoid using grey water on plants that prefer more acidic soil, since water is alkaline.
  • It is important to filter the water from the kitchen to remove oils and fats.
  • Do not reuse water used for washing clothes and clothes used in working with chemicals.

With a creative pipeline an underground irrigation system using grey water can water the garden without any effort.


Reference: Leganes, Lucia. Sustainable Solutions: Water Use in Permaculture. Ed Lizard. 1.ed.Pirenópolis, Texas, 2007.Note: Full copy of Pp. 16 to 19