The basics of a simple domestic grey water irrigation system

Whenever you shower or bath, the used ‘grey water’ is usually directed down the drain to the sewers or French Drain.  Why not send gray water to a water tank and then use it to irrigate your garden?

grey water tank

Water tank where grey water form a shower is temporarily stored then pumped out as irrigation water

Grey water is by definition, the water used in a household that is not ‘black water’ from toilets/urinals.  Greywater includes bathing/showering water, water from basins/sinks and laundry water.  For a simple greywater irrigation system, the source water should be limited to bathing/showering/hand-washing water.  Water from kitchens and dishwashers may have bigger particles that could clog a system.  Laundry water should only be used if phosphate-free detergents are used.

A basic grey water irrigation system consists of diverting water from baths and showers to a temporary holding tank (this can be a drum or small water tank).  A submersible pump is placed inside the water tank and is activated by a float switch, i.e. when the water in the water tank reaches a certain level, the pump switches on.  This water is then pumped out of the water tank to a pipe that irrigates the garden or lawn.

Here are a few important points to ensure the greywater irrigation system works properly:

  • Never store grey water longer than a day.  Grey water contains a certain load of bacteria and if stored for any length of time it will, unless treated, become foul-smelling and a possible health hazard.  This is why the grey water should be pumped out of the water tank as it get there.
  • Install a coarse sieve or filter before the grey water enters the water tank to catch hair and other larger particles.  Is ensures that the submersible pump is not blocked up and also ensures the irrigation head is not blocked.
  • Use a moveable irrigation pipe with a Gardena-type watering head/sprinkler attached – these operate at low pressure and are not blocked easily.
  • Move the sprinkler daily so that all parts of the lawn/garden receive irrigation.
  • Do not use overhead grey water to irrigate vegetables (ie. Do not let the greywater come into contact with the edible parts of the fruits/vegetables)

Simple greywater irrigation systems are easy to design and build – the simplest being the bucket in bath/shower method.  Professionally designed and installed grey water systems are also available.

grey water irrigation

Gardena-type irrigation head operates at low pressure and does not block easily

Grey water has many nutrients that plants require and so fertilizer applications on the lawn/garden can be reduced.  During water restrictions, your garden and lawn will continue to thrive as long as somebody in the household is taking a daily bath/shower (some municipalities may require a sign stating ‘grey water irrigation in use’.  Grey water irrigation also reduces water bills so can so money too…and you can enjoy a longer shower without feeling guilty.

Grey water systems, in combination with rain water tanks, can make many homes and businesses virtually water self-sufficient.

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