Choosing The Right Size Rainwater Tank: Buyers Guide

One of the best ways to prevent running out of rainwater is to design your own rain harvesting system to harvest the volumes of water you need. Choosing the right size water rainwater tank is one of the things for this.

As well as the rainwater tank, it will also depend on the following as to how much rainwater you can harvest as it depends on the average rainfall in your local area, the roof area from which you can collect water, the area which you can site a rainwater tank and the amount of water you use as this will determine how much you will need to store.

Your areas average rainfall

There are many online sources for this information – the Met Office has a rainfall radar here – which will help to determine how much rainfall you can harvest.  If you use more water than you get in your local area you may need to consider whether you get a larger tank or whether a mains top-up valve will be required.

In the UK roughly the same amount of rain falls each year, however, some spring and summers can be better than usual and autumn and winters can be drier than average so a large enough tank will be essential as not to run out of water.

Your roof size to collect rainwater from

As a guide, 1mm of rainwater falling on 1 square metre of roof equals 1 litre of water, so how much rainwater you can collect will be dependent on the size of the roof.  You will also need to consider if you can collect wart from all the roof if maybe only in some areas as depending on where downpipes come down from the roof, collecting water from all the roof may not be possible without a lot of alterations to existing guttering.

View our article on calculating your roof surface area for rain harvesting here

How much water do you use?

According to the CCW and the table below usage of water is as follows in the UK as an average. Household water use varies enormously depending on the number of people in a house and their personal needs with often the biggest user of water being toilets, washing and watering the garden.

Annual Water Usage in Cubic Metres
Number of People Living at Home Low Average High
1 45 66 100
2 55 110 136
3 82 136 175
4 110 165 210
5 136 182 245
6 155 200 265


Where to site your rainwater tank

One factor for rainwater harvesting is where do you site the tank. A 1000 litres is approximately 1 m3 and will need to be put on a concrete pad if this is an above ground tank. The top of the tank will require to be lower than the gutter to get a fall into the tank. Provision will also need to be made for rainwater filter as this will be required to filter out leaves and moss from the water before it goes into the tank.  View more details here.


View more detail on our underground tanks here

The Right Size Rainwater Tank

With the above details and calculations on how to calculate how much rainwater you can save, deciding the right size rainwater tank could not be easier. Enduramaxx works with several rainwater system installers so if you need help or pricing for an installed system please get in touch.

View more of our vertical rainwater tanks here.

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