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How New Zealand can take advantage of its rainfall

Posted by MARTIN PFAFF on

Currently and in the last month some parts of New Zealand had torrential rainfall, after previous droughts in part of the country. How can the country make better use of the rain?


What is rainwater harvesting and how does it work?

Rainwater harvesting is the capture, storage and use of rainwater. Anybody can do it and it can be designed and customized to suit the needs of the user (potable water from rainwater for example).

There are several types of rainwater harvesting systems, the following three are the main ones:

In-situ rainwater harvesting refers to the capture of rainwater where it falls. This system is useful in agricultural production systems where micro-catchments are used. For example Zai Pits ( Wikipedia Zai-Pits).

Run-off catchment is another rainwater harvesting system. Rainwater running of surfaces is channeled through pipes or trenches and collected in storage structures like tanks, ponds, swales (Wikipedia Swale ) and dams, to be used at a later stage or for attenuation and/or infiltration.

Then there are roof catchment systems. These involve capturing rainwater from roof tops and storing it either above or below ground tanks made from plastic, concrete or metal. 

Some facts:

  • In New Zealand around 10% of the population depend on roof collected rainwater.
  • ~ 18% of total water consumption is used for flushing the toilet (domestic).
  • ~ 23% of total water consumption is used for the washing machine (domestic).
  • ~ 41% ( probably more if you add garden irrigation and outdoor use)  of total water consumption could be covered by rainwater
  • ~ 27% of total water consumption is used for showering (domestic)
  • Average water consumption per person in New Zealand  227 liters / day (Learnz). Water consumption varies quite significantly between the regions (Queenstown Lakes District Council 416 liter/day)

Advantages of Rainwater Harvesting

1. Low-cost Maintenance
You really don’t need to invest much money to keep the systems going. Purifying the water is not necessary if you don’t intend to drink the water.

2. Lower Water Bills
You can use your collected rainwater for flushing toilets, washing your clothes, and watering the garden. This’ll help in keeping your water bills to a minimum. (Sample system

3. Great for Irrigation
Rainwater is pure rainwater without any added chemicals into it so you can make sure that this is reliable for irrigation. (Sample System

4. Reduces Ground Water Demand
As our population increases, so does the demand for water. In many areas, we are reliant on dams, rivers  and aquifers for our water sources.

5. Reduces Soil Erosion and Floods
By collecting rainwater, you can minimize the likelihood of flooding around your home and reduce the load on the council stormwater system.

6. Multi-Purpose
You can use rainwater in flushing down toilets, washing your cars and motorcycles, and etc. (Sample System)

Disadvantages of Rainwater Harvesting

1. Unreliable Rainfall
Rain doesn’t fall every day making it hard for you to collect some daily. However, for example, Auckland and other part of the country does not suffer from this compared to other centers.

2. Starting Costs
If you choose to have a rain harvesting system, then the time to implement these systems is when you are building your home as the additional costs are recovered quicker. Allocating funds for a system installed in your home is money well spent and will add value to your home.

3. Chemical roof seepage
Some roof coatings may contain harmful chemicals so it is advisable to talk with one of our consultants first to ensure your roof meets the guidelines.

5. Storage limits
There is a practical limit to how much water you can store on your property and is often limited by your section size and appropriate locations for the tanks . Especially in winter, the rain captured will be greater than the capacity of the tank. Rainwater tanks have to be designed to deal with this situation and to release the excess water to the council stormwater system  in accordance with council requirements.


Rainwater Harvesting is a win-win situation for building owners, councils and the environment.

We can give you advice what systems will suit your needs and what is involved.   /  / + 64 3 2600 589


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