What we'll ask when you apply for the discount

When you apply for the discount, we'll ask you:
  • to measure some areas on your property
  • the capacity of any rainwater tanks and what they're connected to
  • about your infiltration system.

We'll ask you for some measurements to help us work out how much stormwater is staying on your property. It's a good idea to get a pen and paper before you start.

You'll need to tell us the total area of your:

  • property
  • roof
  • hard surfaces
  • soft surfaces.

If you have a rainwater tank, you'll also need to tell us the size of the roof area that drains to it.

If you have an infiltration system, you'll need to tell us the size of the:
  • hard surface area that drains to it
  • lawn or garden area within the system
  • raingarden (if you have one).

How you measure the areas

You may already know the size of your property. If you do, you may be able to estimate the size of your roof and other areas on your property.

If you need an easy way to measure areas online,  Six maps will help you.

In the top left hand corner, choose 'Advanced search' from the 'Search' drop-down box.

Now enter your address, zoom in and you're ready to measure.

Let's measure!

Select the   m2  area tool and click each corner of the area you're measuring. 

Double click the last corner and your measurements will appear on the bottom left-hand side of your screen.

You may find the capacity printed on the side of it - 2,000 litres or 5,000 litres for instance.

If you have the receipt for your tank, it might show the size on it.

How to find out your tank size

Rectangular tank 

Simply measure the length, width and height of the tank in metres. Then use this calculation:

Length x width x height x 1,000 = your tank's capacity 

For example

1 metre x 1 metre x 2 metres x 1,000 = 2,000 litres

Round tank

Simply measure the diameter and height of the tank in metres. Then use this calculation:

Diameter x diameter x height x 0.7857 x 1,000 = your tank's capacity

For example

1.5 metres x 1.5 metres x 2 metres x 0.7857 x 1,000 = 3,500 litres

Working out what your tank's connected to can be a little tricky.

Here are some tips to help you.

  • Look for signs next to pipes or taps. They should say 'don't drink' or have a symbol that shows they're connected to a rainwater tank.
  • Look for two pipes for cold water that connect to your toilet and washing machine. One should be marked 'rainwater' and the other 'potable' or 'drinking'.
  • Run your washing machine, but don't use any other water. Check your water meter to see if the dials are turning when your machine is drawing water. If they're not, your washing machine is connected to your rainwater tank.
  • Ask a plumber to check if your hot water system is connected to your tank. You can't easily see these connections and they're not common.

    Rainwater 'do not drink' sign next to tap

    You might have a sign like this near your outside taps.

An infiltration system is a specially designed area of lawn or garden that allows stormwater run-off from hard surfaces to soak into the ground.

This reduces the impact of run-off from hard surfaces such as driveways and roofs. Sometimes an infiltration system may also include a raingarden. 


A raingarden is a special part of your infiltration system that typically allows water to pond on the surface and slowly soak into the soil.

It's also possible to store water underground instead of on the surface. 

Infiltration system with a raingarden

If you have an infiltration system with a raingarden, the stormwater on your property may flow from your roof like this.

Girl with a recycle symbol on her tshirt

Stopping stormwater leaving your property helps the environment.

Ready to apply?

Apply for a discount on your stormwater charges now!