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What Size Water Storage Tank Do I Need?

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People get water storage tanks for a number of different reasons. It might be that they are wanting to store drinking water from a spring or borehole, it might be that they want to harvest and store rainwater, or maybe store water in an above-ground water storage tank. Water storage tanks, however, come in several different sizes, so it is important that you know what size to get.

When you are considering getting a water storage tank, you must think about how much water that you are likely to need, and then calculate the best size for you to ensure that you will not run out of water. In the UK, water tank volumes are measured in litres.

Key Considerations

The main consideration that you need to make when it comes to choosing the best size of water storage tank is how much water you are likely to need.

Of course, everybody is different and uses different amounts of water according to their lifestyle, the amount of time that they are spending in the building, etc. When it comes to calculating the best size of water storage tank, however, using average water use estimates is usually sufficient.

It is estimated that the average person uses about 150L of water per day. This figure takes into account, drinking, washing, laundry, flushing toilets etc. and can be multiplied by the number of people in the house to give an estimate of the total water requirement. Generally speaking, the calculation of the number of people in the house is based on the number of bedrooms that are present.


When it comes to rainwater harvesting systems, you should also consider the amount of rainfall that you are going to have. If, for example, you live in a very arid place, with an average rainfall of only 400mm, you will need a much larger water tank than somewhere that gets 1000mm.  London, for example, has an average rainfall of about 592mm, and Glasgow, about 1245mm.

With rainwater harvesting, you will also need to take the roof area size into consideration. These will both affect how much water can be collected – and, of course, whether you will need extra water supply – and tanks!

What Else Should I Know?

If you are thinking about getting a rainwater harvesting system, you should also consider how much reserve water you need. We can never know how much rain we will get for certain, so it is recommended that you have some in reserve. This will also affect the size of the water tank that you need. Most people recommend that you have at least 18 days’ worth of water – normally around 21 days to be safe (about three weeks), which is about an extra 2700L of water per person. If you cannot achieve a tank of this capacity you can always opt for a tank or system which has a mains top up facility.

Thursday 29th July 2021
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