Which Size Water Tank Should I Buy?

Download Which Size Water Tank Should I Buy? PDFWhich Size Water Tank Should I Buy? (PDF Version)

Which Water Tank Size Should I Buy?

Rainwater is a valuable natural resource in Australia and the opportunity for harvesting it will vary depending upon your location.

Thankfully, many developed properties have access to a reticulated (mains) water supply. You may not need to harvest rainwater, nonetheless mains water usage can be lowered by installing a rainwater tank.

A main question anyone looking to install a water tank must answer is what size tank should be installed? This article is intended to help you answer this question and hopefully by the end you will have a good idea.

Amount of Water Harvestable

In many developed areas of Australia, yearly precipitation often well exceeds 500 millimetres.  According the Australian Bureau of Meteorology (BOM) the average mean for Summer is about 210mm. You can find out your exact rainfall on BOM’s website.

It is important to know that 1 millimetre of rainwater falling on 1m2 of roof yields 1 litre of water. If you have a roof size of 200m2 that you are using to harvest rainwater from, then over summer if we assume you receive 210mm of rain you would be able to harvest 42,000 litres of water (200m2 * 210mm). This is a conservative estimate—you might be able to harvest much more from your roof, and some locations may pick up such rainfall within just a few weeks.

Amount of Water Consumed

Since rain often falls over a few days and is rarely evenly spread out over a month, you want to ensure your tank is big enough to harvest water when it does rain. In many instances then, a better method for calculating the best tank size is how much water you will consume.

One person in your household will typically consume around 250L per day. The Australian Government’s YourHome recommend plumbing in 5,000 to 20,000 litres to have water supply needs met for an average household with 2 adults and 2 children. If you would like to more accurately work out your water usage, feel free to use National Poly Industries’ online water usage calculator.

To be domestically self-sufficient, then a suitable water tank size based upon the above information would probably a 5,000 gallon (22,700 litre) water tank. This is definitely one of our most popular tank sizes. Being a popular size, many manufacturers compete to provide the best price. As such, tanks around this size will normally give you the best dollar per litre.

National Poly Industries sell a wide variety of water tanks in different shapes, colours and sizes. Tanks are made to meet and exceed the highest Australian standards and backed by a generous warranty. If you are interested in a rainwater tank, contact us for a free no-obligation quote.