Grey Water Systems


Grey water is the waste water that comes from your bathroom, laundry, and kitchen. Water from the toilet is referred to as ‘Black water’ and cannot be recycled in household systems. Some sources do refer to the water from your kitchen as black water this is mainly because the food scraps that end up down your sink can be a source of risk for vermin and disease. For the purposes of this website I will deal firstly with grey water in general, then follow up with some more specific information regarding kitchen waste.

Why recycle grey water in the first place?  Currently in the average NZ household between 55% and 75% of water use is through the laundry and bathroom (excluding the toilet) Research shows that a NZ Adult uses about 180 litres of water per day. This is a lot of potential water that could be used effectively on your garden – even to grow food. When planning our grey water system we realised we could keep an extra 25 fruit trees well watered through the summer months, with water which had just been going into our septic tank.

Water which ends up in our sewerage systems adds to the amount of waste which needs to be processed. Most of this water could easily be recycled, thus reducing the burden on these systems, as well as reusing the water in a productive way such as watering trees and gardens.

When considering a grey water system it is important to also consider what you put in your water when using it i.e: What kinds of soaps, cleaners, shampoos etc do you use? In my experience bringing these soaps etc back to the basics has several other advantages too;

  • Saving you money
  • Healthier for you and your family
  • Healthier for the environment
  • Less clutter in your cleaning cupboards and bathroom.

The main problem with many of the commercial soaps etc are phosphates.  Phosphates entering into our waterways can lead to “Eutrophication” this process in nature happens over thousands of years turning water bodies into natural wetlands and swamps. The increase in nutrients leads to increased plant growth which leads to plants dying quicker than they can be decomposed. This dead plant material builds up creating shallower water. This in turn causes the water to heat up which means there is less oxygen in the water. The problem with human use and disposal of phosphates is that this process is speeded up well beyond what nature can handle.

Finding phosphate free cleaners, soaps etc is relatively easy now with plenty of well labelled options in the shops. I find the’ eco’ store range particularly good. Baking soda and white vinegar fulfill all my main cleaning needs with the occasional drop of essential oil. Check labels on your shampoos there are plenty of choices.

Another issue can be antibacterial cleaners. Water bodies and soils like our own bodies rely on a range of good bacteria to maintain a healthy system.  Research I have found suggests that there are no health benefits to antibacterial cleaners on the market and much supporting evidence of harm from such things as the creation of antibiotic resistant bacteria. Check out for more information.

A frog on our water lily

A home for our passion fruit

Setting up a greywater system:

A grey water system could be as simple as collecting from your bathroom into a holding tank then piping the water from here out to a group of trees. the problem here is greywater sitting like this will become smelly and what happens in winter when you might not have a use for this water. You could simply redivert it back to your old system during the winter months. Sand and gravel offer some filtering options, so too do certain plants. (some of these are listed below)

Frog on a lily

Frog on a lily

Our system:

In designing our system we were lucky to have some good equipment already to hand. This included an old concrete lined corrugated iron tank (1000 litres) A flow form (which had a past life in making aerated compost brews), A farm trough, and a small 120 litre rectangular trough. We bought two round farm troughs (one small enough to just fit in the top of the big tank) a small submersible pump, some 32ml pipe and a solar pump. Sounds like a lot of equipment!

Our system did end up being quite a project, but has become a lot more than just a grey water recycling system. We live on very dry free draining flat land with no natural wetland or other water bodies. This system has given us an extra layer of diversity….Water we can watch and hear, animal life including frogs, and the chance to plant species such as Manuka which our dry soils would not normally allow us to do.

How does it work? The water from our bath, basin, washing machine and kitchen first enters a small the 120 litre trough next to the house (large particles are caught in netting to go to wormfarm) the submersible pump comes on when the water reaches a certain level, and pumps it through the 32ml pipe into the top of the large tank….This tank is full of sand and gravel which filters the water as it moves through and out into the first trough. This trough has a large amount of straw as well as water cress and azolla. Water overflows from this trough into the second trough in which we have planted a waterlily which is thriving. The system would work well left at this with irrigation coming from this last trough. We decided to go a bit further. In our system the water is pumped via solar from this trough up to a small trough sitting inside the first large tank. From here the water flows naturally down through the flowform and is aerated before falling like a waterfall back into the waterlily trough. This way we can keep the water recycling and create the bonus water feature.

Since building this system we have had a least three frogs settle round our ponds, The passion fruit is thriving on the surface of the tank, three young manuka I grew from cuttings now have a home and plans are well underway for planting up around the system.

We have used water out of the trough for watering some of the vege gardens and fruit trees nearby. It took us awhile to start this project but has been well worth the effort.

Plants for Greywater systems:

IN WATER: water cress, raupo, duck weed, azolla
MOIST EDGES: Oio oio, Carex (virgata, secta and geminata)
MOIST TO DRY EDGES: Manuka, Flax (Tenax species), Toe toe, Cabbage trees , Karamu