Rain Water Harvesting in NZ

April’s 2012 NZ Herald Element Magazine has an excellent article that explains how to use water smartly in New Zealand homes.

The article is written by Johann Bernhardt
is local expert on Sustainable Housing and author of

‘A Deeper Shade of Green’ – Sustainable Urban Development, Building and Architecture in New Zealand

The water we use in our homes is now metered and charged for across Auckland and in other cities.

With the average household in Auckland spending $750 a year for their water/ wastewater bill, we have a perfect reason to consider opportunities to save water and dollars at the same time.

Water, along with food, sunlight and air, is vital for our survival. Most parts of this ‘land of the long white cloud’ are blessed with copious amounts of rainwater. Yet water shortages occur and occasions where demand for potable water outstrips supply are increasing.

How can that be?

For a long time we have treated water as a free and abundant commodity and haven’t really looked after it the way it deserves. In addition, increasing water needs for energy generation, farming and domestic supply all have affected the quality and availability of water. Our cities are covered with impermeable surfaces sending precious rainwater straight into streams and harbours instead of allowing it to percolate through the soil, replenishing aquifers in the process.

Here’s where we can help:

There are two main ways to reduce our dependence on town supply – demand management (use water wisely) and rainwater harvesting and reuse.

Demand management

The best bang for your buck is to save water by installing water saving devices and by keeping an eye on our habits.
Inexpensive, low-flow shower heads can be installed in the shower to reduce flow rates from over 10 litres per minute to between 7.5 and 9 litres.
The same can be done with kitchen, laundry and bathroom taps (for purchases of such devices check ecomatters.org.nz orsafewater.co.nz).

When buying new appliances like washing machines and dishwashers it pays to check the star rating of the Water Efficiency Labelling Scheme (WELS) the more blue stars on the label, the lower the water consumption.

Whether in a new house design or the renovation of an existing house, one of the most beneficial steps to take is to locate kitchen, laundry and bathrooms as closely together as possible and to place the hot water cylinder in their vicinity.

If toilet cisterns are to be replaced as part of a renovation, it pays to install a dual flush system that uses only three litres per flush (as opposed to the 15 litres that older cisterns might use). If retaining an existing cistern, savings can be made by installing a ‘Gizmo’ cistern flush limiter. The cost of a Gizmo is minimal, you can fit it yourself and the gains can be considerable.

Fix leaking taps and pipes

Common sense can save water: turn off the tap while brushing your teeth and fill the kettle with only the amount of water you need.

Rainwater Harvesting

We can harvest rainwater by installing a tank that fills from the roof gutters. When designing a new house, it is a no-brainer to install a tank, preferably over 10000l, but a 4500l tank (1000 gallons) is a good start. Connect this to as many downpipes around the house as possible and use the water in the garden and in the house for toilet flushing or clothes washing. In this case, dual plumbing will have to be installed in the house which is not difficult to do at the construction stage.

It is more difficult and costly, however, when retrofitting a tank to an existing house. It also requires building consent. If that cost is prohibitive, a more economical option is to use a smaller, slim-line rainwater tank which fits under the eaves, and to use the water only for watering the garden (no consent required).

Upgrading rainwater to be used for drinking purposes makes sense mainly in areas where there is no reticulated water supply as the required treatment is not only expensive to install but also to run. Building consent is also required for this.

Water Heating

The positioning of the hot water cylinder close to wet areas like the kitchen, laundry and bathrooms can not only lower water consumption but also reduce the energy needed to heat the water.

If you want to lower the on going energy costs for water heating, here are three good options:

  • Solar hot water panels generate more hot water than we need in summer, but not enough in winter, when the hot water has to be topped up regularly by electricity, wood (see below) or gas.
  • Water-heating heat pumps work all year round and don’t need sunshine in winter to generate hot water. This makes them more economical in winter but not as productive as solar hot water panels in summer.
  • A third water heating system is the good old wetback. The water cylinder is connected directly to a free-standing fireplace and the water is circulated through the system.

The woodburner needs to have a 65 per cent energy efficiency rate and the cylinder needs to be elevated to the fireplace to allow the hot water to rise into the cylinder.

For more information on all these topics Auckland Council provides free and independent eco design advice. Phone 0508 326-337.