The 2 Minute Guide to Greywater

There is a heck of a lot of information of up to date information on this website. You could spend hours here.

BUT – you might only have a passing interest in greywater – and that’s fine. Greywater may not be a viable solution for you.

This is a very basic overview. If you find it interesting, then read further into the more detailed pages.

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

The most important concept to understand about greywater is that pouring 5 gallons into a hole in the ground every day does not mean you are saving gallons of water.If the plant only needs 1 gallon per day, you have only saved 1 gallon.

This sounds simple, and logical, but many people lose track of this fact when designing a greywater re-use system.


Greywater 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 greywater each day.
  • A family of 4 produce enough greywater to irrigate over 2,400 sq ft of garden in a semi-dry climate such as Southern California.
  • Untreated greywater must be used within 24 hours, otherwise bacteria can multiply to unsafe levels. Treated greywater can be stored, however in many cases treatment systems are uneconomical for residential properties.
  • In areas with infrequent summer rains, graewater 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.

Greywater for Gardens

Gardens, including fruit and vegetables, do not need fresh potable water. The top level of soil quickly treats the greywater, removing bacteria and contaminants.

Experience has shown ornamental, native and food producing plants thrive on greywater, especially when irrigated every day.
Sensible precautions should be taken, such as eco-friendly detergents, and avoiding the use of toxic cleaners with ingredients such as bleach, boron and sodium.

Irrigating with Greywater

The most basic irrigation method is using buckets to collect and distribute greywater. 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 greywater irrigation 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 (not covered by warranty). Due to the limited number of irrigation outlets, it is also inefficient, wasting significant amounts of greywater.

Diverting Greywater

  • If a new house is being constructed on a slab, greywater stub outs should be installed before the slab is laid. If not 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 greywater 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 greywater dripperlines are easier to install, but should include a surge tank (55 gallons or more) to allow greywater more time to disperse through the drippers.
  • Washing machine greywater can be gravity irrigated in most houses where the washing machine is not in a basement. The washing machine pump is not designed be used to pressurize an irrigation system.
  • Pressurized (pumped) greywater dripperline systems require only small pumping cisterns, as a well designed greywater pumping unit will irrigate at a faster rate than graywater is generated by two showers, or a shower and a washing machine used simultaneously.

A pressurized system can easily irrigate a 7,000 sq ft property in a single zone (subject to sufficient greywater production in the house). In most cases, greywater can be pumped 25′ uphill and an unlimited distance downhill, without the need for a secondary pumping unit.

Pump Misinformation

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

  • While gravity driven irrigation systems (especially greywater dripperlines) are inexpensive and highly efficient, the ideal system for whole of house graywater re-use, (and certainly where the irrigation field/s are uphill from the greywater source), a pumping station will be required. In the past these were expensive, but quality products are now available for around $500-$600.
  • Tens of thousands of greywater pumping and irrigation systems have been installed in the hot and dry Australian climate, without requiring significant maintenance.

Some of the sillier claims still promoted on current websites are:

  • Pumps don’t work long without filtration.Dirty water submersible pumps are designed for …dirty water. They use an impeller to create a whirlpool in the pump and force the water out with little contact with the impeller.They are designed to pump soft solids up to 1 1/2″ or more in size. About 10 years ago there was a common perception in Australia that greywater had to be filtered before the pump, to preserve the pump.This has since been proven false – in over 6,000 systems manufactured and sold in Australia by Just Water Savers (Australia), not one pump has been bound by hair or lint, and this is with filtration after the pump.
  • Pumps use a lot of electricity, typically being between the number 2 and 5 energy consumer within the home.A 660 Watt pump, providing more than enough power for residential greywater applications, will typically run for 1/2 hour per day, in total, with 4 people living at the house, and actually only uses 450 Watts during operation. Therefore the total daily power usage is 0.25 kilowatt hours.At say, 11 cents per kilowatt hour (2007 USA average), this comes to a cost of 2.8 cents per day, or $6.70 per year (60.8 kWh). As comparison, this is less than the amount of power consumed by a DVD player, hardly in the top 5 energy consumers in the home.Overall the power usage represents 0.6% of the average home power consumption (based on 2001 USA household electricity statistics). This calculation is based on a greywater system connected to all shower / bath and laundry waste, in operation for 9 months of the year.