The right tank size depends on three things: how much roof you can collect from, how much it rains where you live, and how much water you want to use. Here's an easy way to work it out.
Step 1: Work out your roof area
Only the part of the roof that drains into the gutter feeding your tank counts. Measure the length and width of that section of roof from the ground, using the outside of the gutters. A typical Melbourne house might have 50 to 100 square metres draining to one downpipe.
Step 2: Check your rainfall
Every millimetre of rain that falls on one square metre of roof gives you about one litre of water. Melbourne averages roughly 600 to 650mm of rain a year, a little over 50mm a month on average. Regional areas vary, so check the Bureau of Meteorology for your town.
Step 3: Do the sum
Roof area x rainfall x 0.8 = litres you can collect. The 0.8 allows for water lost to evaporation, splashing and first flush.
Example: 60 square metres of roof x 50mm in an average month x 0.8 = 2,400 litres a month. A single good downpour of 20mm on the same roof gives you about 960 litres.
Step 4: Think about how you'll use it
- Garden only: A vegetable garden can use 10 to 20 litres per square metre a week in summer. A few raised beds and pots will happily run off a 1,000 to 2,000 litre tank.
- Garden plus washing the car or topping up ponds: Look at 2,000 to 5,000 litres.
- Plumbed into the toilet or laundry: You'll want a larger tank and a pump, and a plumber to connect it.
Bigger isn't always better
A tank only helps if it fills. If your roof area is small, a huge tank will sit half empty. Match the tank to what your roof can collect, and to the space you have to put it.
What fits your space
Space is usually the real limit. Our steel tanks are made to order in Melbourne from BlueScope AQUAPLATE® steel in four shapes:
- Slimline: 550mm wide, for side paths and fence lines. For example, 1,100 litres in a 550 x 1400 x 1560mm tank for $1,785.
- Modline: a little wider with squarer ends. For example, 1,634 litres for $1,940.
- Square and round tanks, for when you have more room. These are made to order, and Find My Tank shows the price for your size.
The easiest way to choose is Find My Tank. Enter the length, width and height of your space and it shows every tank that fits, with litres and price. Delivery is priced per tank by distance, and you can check yours on our delivery map.