Under the Choko Tree By Nevin Sweeney

Building a Household Waste Water System

A friend of mine, Greg, put together a system to treat the greywater coming out of his bath, shower and laundry areas. It was part of a larger plan to capture and store rainwater from the roof, pump it to the house for toilet flushing and use in the laundry and bathroom, then capture, treat and re-use the greywater produced from those areas.

He made the decision to install his water management system as a result of attending a permaculture course, which helped him focus on being more water wise and maximising the use he was getting out of the water resources available to him. His system makes his household more self-reliant as well, so that in the event of a failure occurring in the reticulated water system he and his family would be insulated from the effects of those failures.

He also hates waste and his system reduces water wastage to a minimum. The system does not treat or recycle any black water and has been operating for three years.

Installation

The first part of the process was to run pipes from the drainage system for the laundry and bathrooms to a central collection area. In the central collection area a 220 litre above ground pit was installed to act as a holding tank before the greywater was pumped further on in the process. A 240v submersible pump was installed to complete this part of the system. Fortunately the house is up on piers so this could be done fairly simply but due to the need for subsequent inspection a plumber was retained for this part of the project.

Two outlets were plumbed into the pit. One on the western side towards the top of the pit accepts the output from the pump and one at the bottom of the southern side of the pit is only used for washing out the pit and is plumbed through to a flower bed in the front yard (no edible species). The output from the pump is fed into 40mm ID blue line polypipe.

Pipes from the laundry and bathroom into the pit

Output, through the pump, to the treatment area

Pit drain to allow cleaning

The blue line polypipe runs in a trench along the side fence of the property all the way to the back fence (which is the highest part of the property) where it curves up so that it discharges into the water treatment area. The water treatment area was originally a pile of rocks which allowed the water to be oxygenated and exposed to the ultraviolet radiation from the sun to achieve a degree of biological contamination.

Support structure for spa

It proved difficult to direct the water output using this technique, so two (approx. 200 litre) bathtubs were installed in series but even this proved to be insufficient capacity and a disused 600 litre spa was installed.

Hose discharging into the spa

The set up now is such that the pipe discharges into the spa, with an air gap to prevent the greywater siphoning back toward the house. The spa has two discharge points, one above the other, towards the top of the spa and into the first bathtub. The top discharge point comes into play if the greywater flow rate exceeds the ability of the lower one to prevent the spa from overflowing. The first bath has a single discharge point towards the top of the bath, allowing discharge into the second bathtub and the second bathtub has a discharge point plumbed through a valve and a pipe. The now purified greywater is discharged into the pipe, which can direct the flow under gravity to any area of an existing food forest.

Water drain from spa into first bathtub

The spa and the baths are half filled with gravel to provide a substrate for aerobic water cleaning bacteria to colonise and the discharge points are set up such that the amount of water left in the spa and bathtubs is always below the level of the gravel.The spa and bathtubs have been levelled so that they fall slightly towards the next reservior so that in the event of overflow, they will still overflow into the next reservior rather than overflowing out of the system.  The spa and bathtubs are planted out with taro and papyrus which is harvested on a quarterly basis to provide biomass for compost making.

Drain from first bathtub into second bathtub

Water discharge from second bathtub onto soil via hose

Hose distributing treated water to food forest floor

Ditto

How does it Work?

Greg says his system works so well that he has to remember to check it regularly just in case, because it runs so well with minimum inspection or intervention from him. The system allows rainwater captured from the roof to provide three services before re-joining the water cycle –

  1. The water is used initially to wash clothes and people inside the house,
  2. The greywater grows biomass for composting as part of the purification process,
  3. The purified greywater is used to irrigate a food forest

Vegetation used for composting

Greg’s comment is that if he can do it, anyone can but he also recommends two books which he found very helpful during the research phase of the project –

  • Create an Oasis with Greywater by Art Ludwig (ISBN 9780964343399), and
  • Water Storage – Tanks, Cisterns Aquifers and Ponds by Art Ludwig (ISBN 9780964343368)

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