Setting up a rainwater tank

Rain harvesting diagram -  courtesy of Marley

Rain harvesting diagram - courtesy of Marley

So you want to install a rainwater tank?

Diverting rainwater from your downpipe to a storage tank is a great way to reduce your use of treated water especially for gardening or outdoor cleaning.

It can also increase your options in the event of as water supply emergency.

It can be relatively simple to install a kit that diverts the 'first flush' of rain from your roof and gutters, which contains most of the contaminants, away from your tank, feeds clean water into your tank, then directs overflow back into your stormwater system.

We encourage the installation of rainwater tanks, including for use in an emergency, such as an earthquake*.

The Wellington Region Emergency Management Office (WREMO) has partnered with a NZ rainwater tank manufacturer, The Tank Guy, to make a 200 litre water tank and kit available for $105. For more information (and for a handy video on how to install the rainwater tank) visit this website.

We’ve compiled a list of Frequently Asked Questions (see below) to provide guidance if you’re thinking about installing a rainwater tank.

*In 2011, Greater Wellington Regional Council commissioned research into whether installation of rainwater tanks for toilet flushing and outdoor water use would help defer building a new water storage lake or dam. The results of this research showed that a rainwater tank could provide for a high percentage of a household’s water needs for toilet flushing and outdoor uses. However, widespread installation of tanks would not be cost-effective as an alternative to developing the metropolitan Wellington water supply system. The research also found that rainwater tanks would be good for household emergency resilience.

Frequently asked questions - rainwater tanks

Why should I install a rainwater tank?

How much water would I need for a natural disaster?

What size tank would I need for emergency water storage?

Can I drink water from my rainwater tank?

What can a rainwater tank be made of?

How much do tanks cost?

Where can I buy a rainwater tank?

Do I need planning or building consent?

Does it need to be installed by a professional?

Does my rainwater tank need to be secured in case of an earthquake?

Where can i find more information about rainwater tanks?

Why should I install a rainwater tank?

Rainwater tanks can have multiple uses. They’re good for storing water for watering your garden, washing your car and flushing your toilet. And they’re also an excellent source of emergency water in a natural disaster.

As we saw with the Canterbury earthquakes, a large earthquake can disrupt water supply for weeks or even months.

In the Wellington region, our bulk water mains cross the Wellington Fault six times. It could take a long time to fix all the pipe breaks not only in the bulk water mains but also in the local water pipes. So there could be areas where the water supply is not restored fully for months.

By diverting rainwater from your roof guttering to a rainwater tank, you’ll have your own source of water, even when the water supply system isn’t working.  

Back to top

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 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 – we recommend having 20L per person per day of 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, which means that a smaller tank could be enough – see What size tank would I need for emergency water storage?

Back to top

What size tank would I need for emergency water storage?

Bigger is better!

Research shows that during a Wellington summer with average rainfall, a 750L rainwater tank that is refilled by rain (via a connection to the house roof guttering) could last for around 80 days for a family of three (at 20 litres per person per day). However, during a dry summer, a 750L rainwater tank may only last 13 days for a family of three before it runs dry.

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

See the table below for more information:

Tank size

The number of days that a rainwater tank would provide 20 litres per person per day in a summer with average rainfall

Household occupants

2

3

4

500 Litres

80 days

40 days

30 days

750 Litres

Ongoing*

80 days

55 days

1,000 Litres

Ongoing*

Ongoing*

60 days

2,000 Litres

Ongoing*

*Ongoing means unlikely to run out of water

Back to top

Can I drink the water from my rainwater tank?

Yes you can – but you’ll need to take a few simple precautions. People who live rurally in New Zealand are generally not connected to a town water supply. A large proportion of them would collect rainwater from their roofs as their main source of tap water.

The Ministry of Health has information about managing water quality for households on tank water supply which may prove useful.

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.  For an example of a well setup rainwater tank system, check out the picture at the top of your screen.

Before drinking your emergency water, we recommend either boiling it or adding a few drops of household bleach to the water – see the Ministry of Health website for more information.

*A leaf guard is a screening device that is attached to the top of 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 bird droppings) from your roof, from entering the rainwater tank.  It does this by diverting the first water into a separate small chamber. Once the chamber is full, the rest of the water carries on to the rainwater tank.

Back to top

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'.

Types of tanks:

(Source: www.hg.com.au/product_cat.php?NodeID=198#whatsize - retrieved July 2012)

  • Polyethylene tanks: Commonly known as 'poly' tanks, these tanks come in many sizes and colours and are suitable for both above and below ground use. They last a long time, are UV-resistant, cost less than metal tanks and, because of their lightweight construction, are easy to transport
  • Metal tanks: Metal tanks are light and easy to transport, are suitable for above or below ground use, can be custom made and are usually corrugated or straight rolled. They can be made from a variety of metals including:

- Galvanised steel - zinc-coated Z600 steel (prone to rusting)

- Aquaplate or Colorbond - coloured polymer-coated steel (lasts longest)

- Zincalume - silver-coloured zinc/aluminium-coated steel (prone to rusting)

- Copper and stainless steel - used for specialised applications

  • Concrete tanks: Concrete tanks can be built above or below ground. They're usually made on site and are durable and long lasting. However, they can sometimes crack – especially when they are below ground in clay soil. They're good for preventing algal growth (light can't penetrate) and they keep water cool.  Concrete tanks are generally only available in large sizes – over 9,000 litres
  • Fibreglass tanks: Fibreglass rainwater tanks are resistant to chemical corrosion and are suitable for both ground and stand installations. They are tolerant of extreme temperatures, come in a large range of colours and sizes and, because of their lightweight construction, are easy to transport. Fibreglass tanks can be more expensive than other varieties
  • Bladder tanks (or pillow tanks): Bladder tanks are made of flexible and durable PVC and are designed to fit under floors and decks.  They utilise previously wasted space rather than garden space.  The ground that the bladder tank sits on must be flat
  • Timber tanks: Timber tanks have timber exteriors (including a roof) with a plastic lining.  Smaller tanks can be erected by the homeowner.  They are available in a wide range of sizes

Back to top

How much do tanks cost?

Rainwater tanks come in a variety of sizes and prices.

A 200L rain barrel typically costs around $100–$200. A 5,000L rainwater tank can cost over $2,000. Installation costs (for example leaf guards, first flush diverters, earthworks, pumps for indoor use) and transportation costs are extra. For an example of what installing a rainwater tank for toilet flushing might cost, see an estimate that GWRC sourced in 2012.  Please note that this estimate is based on the following criteria: a flat section with easy access to the rear of the section; hipped roof with a front and rear downpipe; blank wall with grassed area next to rear downpipe suitable for a rainwater tank; a single toilet two metres from tank location; the house on piles giving underfloor access to mains water and toilet cistern supply; and a power supply available from the laundry.

Back to top

Where can I buy a rainwater tank?

There are many retailers that sell rainwater tanks. Tanks less than 1,000 litres in size may be available from your local hardware store with most tanks available to order online.  The products and companies featured in the link below are a starting point to help you find a product that fits your requirements – contact the suppliers directly for detailed information.  

Please note that these suppliers are not endorsed by Wellington Water and Wellington Water accepts no responsibility for the products and services offered by the individual companies.

Companies and their details featured here are subject to change without notice.

Rainwater tank suppliers

Back to top

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 in Lower Hutt, Upper Hutt, Wellington or Porirua.

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 height above ground as well. Call your local council if this applies to your situation

For indoor use

If you're planning to connect your rainwater tank to your toilet or washing machine, you will need a building consent.

This is to ensure pipe entry to the house is properly sealed, and that rainwater from your system can't enter the public water network. You will need a registered plumber to carry out this work for you.

And if you want to use it for drinking, you'll need to have the water treated or purified, and may need an annual inspection. Again, contact your local council's building consents team for details.

Back to top

Does it need to be installed by a professional?

Not necessarily. If you are connecting a rainwater tank to your toilet or laundry, the tank will need to be installed by a qualified tradesman and a building consent is required. Otherwise, most installations can be done by the homeowner – check with the supplier of your rainwater tank.

Back to top

Does my rainwater tank need to be secured in case of an earthquake?

We recommend securing your rainwater tank so that in an earthquake, the contents are not lost – just when you would need it most! The rainwater tank needs to be secured in such a way that it does not cause damage to either your house or your neighbours’ properties.

Talk to your rainwater tank supplier for the best way to secure your tank.

Back to top

Where can I find more information about rainwater tanks?

Check out these links:

smarterhomes.org.nz/water/collecting-and-using-rainwater

www.healthed.govt.nz/resource/water-collection-tanks-and-safe-household-water

The Department of Building and Housing's schedule of exempt building work has details regarding tank construction.

dbh.govt.nz/bc-no-consent-schedule-1#tanks-and

However, please note that your local council may have other applicable guidelines, so if you have any questions, please contact them for guidance.

The Ministry of Health has a series of publications related to drinking water systems

health.govt.nz/our-work/environmental-health/drinking-water/drinking-water-publications

Back to top