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Rainwater Harvesting - harvest and use your own rainwater

Harvest and use your own rainwater

There are many reasons to consider investing in a Rain Harvesting system for your home. Having your own system will allow you to enjoy:

  • Improved drought resilience
  • Alternative water supply during restrictions
  • Cost savings associated with lower water bills
  • Lower environmental footprint
  • Added value to your property
  • Increased self-sufficiency
  • Enhanced building resilience

Consider what size tank you need

To calculate the size of tank you’ll need, consider:

  • the annual rainfall in your area
  • what you intend to use the water for
  • whether you have access to mains water supply.

You don’t need to have a huge tank to make a difference – even a rain barrel will reduce your outdoor water use and provide water in an emergency. Some councils sell these, so check with yours.

For garden watering, you can install either a rain barrel (generally about 240 litres) or a rainwater tank (500 litres +). In areas such as Auckland, with year-round rainfall, a smaller tank might be enough for the garden. If you live in an area with dry summers, or you water your garden a lot, you will need a larger tank.

If you are planning to use rainwater for indoor supply, you will need a larger tank. In areas with year round rain, a 5000-litre tank will provide a good proportion of your water use. In areas with dry summers, you’ll need a much larger tank (10,000 litres +).

If rainwater is your sole source of water, you will need at least a 30,000-litre rainwater tank. Talk to your local suppliers to find out the size that would best suite your climate and household.

Other factors that might influence the size of your tank include:

  • the size of your property – a large garden will need more water
  • the size of the collection area
  • how reliant you are on the water supply
  • how efficient your water using appliances and plumbing fittings are.

If you live in the city and are short of space, you could install a slim-line tank that fits alongside and attaches to a wall on the side of your house. Water is heavy, so even slim-line tanks need to be well supported.

 

Preventing contamination

A leaf filter helps keep your rainwater tank free from larger-sized contamination.

To prevent leaves, droppings and other organic matter from contaminating your rainwater:

  • Use a 'first flush diverter'. This is a simple, inexpensive device that fits on to your downpipe or tank inlet. It prevents the initial flow of contaminant-laden water from the roof entering the tank when it rains. Contaminants drain off to the stormwater, or a suitably planted part of the garden or soakage area.
  • Ensure the tank is tightly covered – this also prevents evaporation.
  • Use a screen over the tank’s inlet pipe to keep out insects, birds and animals.
  • Install gutter screens that prevent debris from entering the gutter but don’t stop water flow. Check that they don’t compromise your roof and gutter warranties and that they can themselves be cleaned easily periodically.

Pumps

A submersible pump will provide the extra boost needed to move water from your tank through your garden hose.

Treating and purifying water for drinking

If you want to drink your rainwater or use it for any household use other than flushing the toilet and washing clothes, you'll need to treat it or purify it. To do this, options include:

  • adding chlorine
  • using a very fine in-line filter or purifier
  • boiling the water for one minute
  • ultraviolet light treatment.

Pumps

A submersible pump will provide the extra boost needed to move water from your tank through your garden hose.

Treating and purifying water for drinking

If you want to drink your rainwater or use it for any household use other than flushing the toilet and washing clothes, you'll need to treat it or purify it. To do this, options include:

  • adding chlorine
  • using a very fine in-line filter or purifier
  • boiling the water for one minute
  • ultraviolet light treatment.



Apply the eight rain harvesting steps

1. Limit sources of contamination

  • Check your roof surface materials and trim overhanging vegetation
  • Install gutter mesh to prevent blockages

2. Plan for volume

  • Consider your annual rainfall, seasonality, roof surface area and rainwater needs
  • Use a Maelstrom filter to minimise water loss and a high level tank overflow to boost storage volume

3. Filter leaves and debris

  • Use Leaf Eater rain heads or a Maelstrom filter to keep leaves, debris and mosquitoes out of your system

4. Divert the first flush

  • Install first flush diverters to keep the most contaminated rainwater out of your rainwater tank

5. Secure the system

  • Use a tank screen and insectproof screens to keep out leaves, mosquitoes and animals
  • Install an air gap to prevent stormwater backflow

6. Manage standing water

  • Use a wet-dry valve or first flush inground diverter to drain your pipes in between rainfall events
  • Install a Maelstrom or solar shield to block sunlight and prevent algae growth

7. Consider a safety net

  • Use an appropriate rainwater filter after your pump to reduce sediment, colour and odour

8. Monitor and maintain

  • Install a tank gauge to monitor your water level and usage
  • Use a Mozzie Stoppa Easy-Clean for simple overflow maintenance
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