Three Waters

In Aotearoa New Zealand we like to divide water into three types:

  • Supply water (which can be potable or non-potable)
  • Storm water
  • Waste water

At least 60 million litres of water are abstracted from the Waikato River every day. This is treated to drinking water standard – at great financial cost. Approximately 500,000l will be drunk, so 59,500,000 litres of water made drinkable will not be consumed. One must ask whether this is a good use of resources and money!

rain harvest

What’s more, most homes have a water collection device on them: a roof and pipes! But we do not harvest it; we just send it straight to stormwater.

Stan Abbott is very knowledgeable about rainwater harvesting. His published materials can be useful for people wishing to learn more about rainwater harvesting. Some links to his work include:

Checklist for a good rainwater collecting system:

  • Clean roof (would you lick it?).
  • Clean and clear gutters.
  • Have slopes on the gutters, to avoid water stagnation.
  • Good tank (Plastic can leach. Concrete is self-healing, maintains a good pH and regulates temperature).
  • Minimise bends and curves in the piping if possible.
  • Have a ‘first flush diverter’, which diverts the first 200 (or so) litres of water, as these will contain the most impurities and sludge.
  • Put the tank out of the way, e.g. under garage or drive.
  • Try to get the water as clean as possible before it enters the tank, as then there is less you have to process afterwards.
  • Have a calming inlet (e.g. at the bottom of the tank) so that it does not splash and disturb water/sediment when it enters.
  • Have tap part the way up the tank, so as to avoid sediment. A 1 micron filter should be sufficient.
  • Install overflow at the bottom, as it will self-clean the water by sucking up sediment.


Managing stormwater

  • If you are harvesting rainwater, you are already storing/managing a lot of it
  • Avoid concrete and impenetrable surfaces, as these result in surface run off and erosion.
  • Only gather the water you will use – let the rest go into the ground.
  • Keep it on land as long as possible. Our modern stormwater management systems try to get stormwater into rivers as quickly as possible, leading to flooding and erosion. If we can slow the rate it enters waterways, the results are less extreme.
waikato river
Waikato River (image from Pixabay)

Managing ‘Waste’ water (‘waste’, because we should reconceptualise it to ‘nutrient-inriched-water)

It can be useful to separate black and grey water.

  • Grey water has high volumes and low toxicity
  • Black water has low volume and high levels of BODs and suspended solids

Blackwater can be sent to a worm farm for processing, before being sent to a reed bed. Grey water can go straight to reed bed.

waste water

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