Guide to greywater systems

We take you through greywater options, from simple diversion to 'Class A' treatment systems.
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  • Updated:2 Jan 2008

02.Two types of system

There are two basic types of system to recycle greywater: diversion devices and treatment systems.

Greywater diversion devices

Using this system, greywater is diverted from its source to the garden. The diversion device could be as simple as a flexible hose that you attach to your washing machine outlet, sending the rinse water into the garden (instead of the drain) whenever it needs watering.

A CHOICE test of the wash water showed it would be bad for most soils to put water containing so much detergent onto your garden.

Moving up a level, simple diverter valves can be plumbed into appropriate outlet pipes, and allow you to manually switch between diverting water through pipes onto the garden, or into the sewer. These cost from around $30.

Other diversion systems include shower to toilet diversion — an option if you have no garden. These are called closed-loop systems, though they’re not approved in some states. More sophisticated diversion systems may include a surge tank, filters and a pump.

  • A surge tank takes the brunt of greywater outflow and ensures the garden won’t be suddenly inundated with hot water or, worse, allow greywater backflow into the house. You need to remove sludge from the tank every six months or so. It should also have an overflow device sending excess water into the sewer.
  • Filters remove hair and other large particles from the water so they don’t clog up your irrigation pipes (which can be an issue with diversion-only installations). They require routine maintenance to clear the filters, and need replacing every 6 to 12 months.
  • A pump may be necessary to get water to all parts of your garden, especially if gravity’s not on your side. You’ll need a power source for it, which may mean getting an outdoor power point installed.

Costs for these more complex greywater diverters range from several hundred to several thousand dollars, depending on what you need in the way of pumps and surge tanks, irrigation equipment and the suitability of your existing plumbing. You’ll also need the services of a licensed plumber, and will most likely need to alert authorities that you have such a system in place.

Untreated greywater should only be used for sub-surface garden irrigation — that is, through a network of pipes buried at least 100 mm below the ground – to reduce the risk of human or animal contact. Pipes carrying untreated greywater must display relevant warning labels. And you can’t store untreated greywater, because the bacteria and other pathogens could multiply to dangerous levels. Use it immediately (or within 24 hours), and if it’s raining, divert it to the sewer.

Greywater treatment systems

These systems collect and treat (and some disinfect) the water to various levels of purity and hygiene. Generally, the higher the treatment level, the higher the cost. Several stages are involved in the treatment of water, starting with the filtration of solids (lint and hair).

Pathogens and unwanted chemicals (such as salts and nutrients) can be removed from the filtered water in several ways, including micro-organisms and chemical treatment. Disinfection by chlorination or UV light is the last stage of the process, though not all systems do this.

We found basic treatment systems for around $4000. The water produced is cleaner than greywater that’s only been filtered, and some of the chemical and nutrient load has been reduced — so it’s kinder on your plants. However, for health reasons it should still be used only for sub-surface irrigation systems for ornamentals and fruit trees, say.

Systems that treat greywater to 'Class A' level (which is considered safe for watering plants intended for eating, but not for drinking or preparing food) cost from around $10,000 up to well over $20,000 including installation. Bear in mind you'll also need to pay considerable maintenance costs — to cover regular service call-outs and filter replacements.

Installation costs tend to escalate if a lot of extra plumbing is required (if your bathroom and laundry pipes are spread all around the house, say) or if pipes are in a concrete slab.

The amount and location of water storage can also affect costs. Installing a system when building a new house (or doing major renovations) tends to be cheaper than retrofitting one. Toilet

The cost of mains water in Australian cities is so low that you’re unlikely to ever recoup the cost of a greywater treatment system. On the other hand, if you consider that a garden makes up about 10% of the value of your home, you might think the cost of a treatment system to keep your garden (and home value) growing during water restrictions is worthwhile.

Treated water can be used in washing machines and toilets, as well as on the garden. If you don’t have much garden to water, or if you don’t need to water it in all seasons, this sort of system may be a more useful option, as you can use the water elsewhere.


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