About Rainwater Harvesting

Diverting rainwater from your downpipe to a storage tank is a great way to conserve water, especially for gardening or outdoor cleaning use. It can also increase your options in the event of a water supply emergency, such as an earthquake.

Why should I install a rainwater tank?

Rainwater tanks offer multiple uses. They’re good for storing water for watering your garden and washing your car. And they’re also an excellent source of emergency water in a natural disaster – although you will need to treat the water if you want to drink it.

As we saw with the Canterbury earthquakes, a large earthquake can disrupt water supply for weeks or even months. Not to mention water contamination that was seen recently in Dunedin and Havelock North.

By diverting rainwater from your roof to a rainwater tank, you’ll have your own source of water, even when the water supply system isn’t working.  It will also mean you can continue to water your garden when water restrictions are in place, as long as you are using your own rainwater supply.

Can I drink the water from my rainwater tank?

No, not without safely treating unfiltered water, your Watersorter Installer can also provide information and assist you with this. For information on how to safely treat unfiltered water from your rainwater tank to use as an emergency drinking supply, visit the Nelson Marlborough District Health Board Website or HealthEd

It is important to ensure that the water going into the rainwater tank is as clean as possible. We recommend installing leaf guards* and first-flush diverters+ on the downpipe leading to your rainwater tank. 

*A leaf guard is a screening device that is attached to your downpipe and prevents leaves and other debris from entering the rainwater collection system.

+First-flush diverters are designed to prevent the first part of the rainfall which picks up most of the dirt, debris and contaminants (such as (such as dust, pollen and bird droppings) from your roof, from entering the rainwater tank. 

It does this by diverting the initial first few millimetres of rainfall into a separate chamber. Once the roof is clean and the chamber is full, the rest of the water carries on to the rainwater tank.

How much water would I need for a natural disaster?

This depends on: (1) how many people there are in your household; and (2) how long it will take to restore the water mains supply network after a natural disaster.

Civil Defence recommends storing a minimum of three litres of water per person per day for seven days – but this is just drinking water for survival.

You will need to store more water for cooking and hygiene – it is recommended you have a minimum of 20L per person per day of emergency stored water for as long as the water supply system isn’t working.

If you have a family of four and the water supply is out for two months, you would need to have stored around 4,800L. A rainwater tank that is connected to your roof guttering system would get replenished every time it rains, so consider your local climate and rainfall whilst thinking about tank sizes.

What size tank would be suitable for household water storage

Bigger is better! For maximum effectiveness, the tank must be connected to the roof guttering of your house so that it can be refilled by rainfall.

The amount of rain you can collect from your roof depends on the size of the roof and your local average rainfall.

The drier your climate, the bigger tank you need to make sure you have enough water to see you through an emergency period or a drought.

If you are looking for a simple system to store water simply for watering the garden, washing the car etc. then a 400-2000 litre tank will usually be more than adequate for your needs. You can of course add more tanks to increase your supply. Gardens use about 20% of a household’s water.

Laundry and toilet flushing uses up to 45% of a household’s water. Talk to Mike about having a plumber hook up your rainwater supply to your toilet and/or laundry.

What can a rainwater tank be made of?

A rainwater tank can be made of a variety of materials.  If the tank is going to be used for drinking water (even just in an emergency situation), the material that it is made from must comply with potable water requirements under AS/NZS 4020 'Products for use in contact with drinking water' and with AS/NZS 2070 'Plastics materials for food contact use'. Check out the product information and comparisons - click here.

Do I need planning or building consent?

For outdoor use - urban areas - If you're installing a typical (say 2,000 litre) tank to collect rainwater for outdoor use only, such as garden watering or emergency supply, then as a general rule you don't need a building consent.

Schedule One of the Building Act list situations where tanks do not require building consent (view here). Please note however that other considerations may apply, such as the resource consent requirements for your area.

For example, if you were planning to put your tank on an elevated platform, you would still need to observe the height and boundary limits that apply in your area, and there are capacity limits relating to the height above ground as well. Your Watersorter Installer will ensure your tank installation is correctly installed subject to council regulations.

Information kindly provided by Nelson City Council

Interested in Rainwater Harvesting? Contact us to find out more about our rainwater tank solutions.  


Check estimated prices for a Rainwater Tank supplied and installed on our Services page