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Graywater A 2 minute overview

This website contains a lot of information about graywater irrigation for gardens. This section is a summary for those that need a quick overview.

Before delving into the concepts, it is important to state that graywater re-use is now relatively easy. New dripperline technology has now made it possible to install a complete residential garden graywater irrigation system (excluding plumbing modifications), to professional standards, in just a few hours.



  • Graywater is waste water from showers, bath, hand basins and the laundry. It does not include water from the toilet, or laundry if the wash includes soiled items such as diapers.
  • The average person generates over 25 gallons of graywater each day.  
  • A family of 4 produce enough graywater to irrigate over 1,600 sq ft of garden in a semi-dry climate such as Southern California.
  • Untreated graywater must be used within 24 hours, otherwise bacteria can multiply to unsafe levels. Treated graywater can be stored, however in most cases treatment systems are uneconomical for residential properties.
  • In areas with infrequent summer rains, graywater is cheaper to harvest than rainwater. If little rain is experienced for a 3 month period, a family of four can re-use over 3,000 gallons per month. An equivalent cistern would need to be at least 9,000 gallons capacity.

Graywater for Gardens


  • Gardens, including fruit and vegetables, do not need fresh potable water. The top level of soil quickly treats the graywater, removing bacteria and contaminants. Experience has shown ornamental, native and food producing plants thrive on graywater, especially when irrigated every day.
  • Sensible precautions should be taken, such as eco friendly detergents, and avoiding the use of toxic cleaners such as bleach, boron and sodium.

Irrigating with Graywater


  • The most basic irrigation method is using buckets to collect and distribute graywater. This method, while inexpensive, is very inefficient, and prone to overwatering.
  • Sub-surface dripperlines are the most efficient method of irrigation, and can make use of capillary action. IrriGRAY dripperline revolutionized graywater irrigaiton in Australia, and now has over 90% of the irrigation market there. It is now manufactured and available here in the US.
  • Because of the capillary effect resulting from daily irrigation, dripperline systems are designed to water the whole garden bed – NOT just individual plants.
  • Laundry to Landscape, popularized in California, is time consuming to establish, and significantly increases the risk of washing machine failure.
  • DIY pump and hose kits, while against the rules in many jurisdictions due to prohibition of graywater aeration, are commonly used in many areas because of their low cost, and ease of installation.

Diverting Graywater


  • If a new house is being constructed on a slab, graywater stubouts should be installed before the slab is laid. If specifically requested before construction commences, it is common for builders to combine waste pipes within the slab (to save cost), rendering the waste water unusable.
  • Older houses, or houses built on piers / stumps, can generally be retro-fitted with a graywater irrigation system.
  • Gravity based irrigation systems, built from standard poly tube or branched drain networks are difficult to design and implement. Ongoing tuning will be required to evenly irrigate the garden area.
  • Gravity based graywater dripperlines are easier to install, but should include a surge tank (55 gallons or more) to allow graywater more time to disperse through the drippers.
  • Washing machine graywater can be gravity irrigated in most houses where the washing machine is not in a basement. The washing machine pump should never be used to pressurize an irrigation system.
  • Pressurized (pumped) graywater dripperline systems require only small pumping cisterns, as a well designed graywater pumping unit will irrigate at a faster rate than graywater is generated by two showers, or a shower and a washing machine.
  • A pressurized system can easily irrigate a 7,000 sq ft property in a single zone (subject to sufficient graywater production in the house). In most cases, graywater can be pumped 25’ uphill and an unlimited distance downhill, without the need for a secondary pumping unit.



  • Much of the information on US websites has been disproven in Australia over the last 5 – 10 years.

  • Tens of thousands of graywater pumping and irrigation systems have been installed in the hot and dry Australian climate, without requiring significant maintenance.

  • These systems cost far less than those previously available in America, and have proven to be resilient.