Calculating the Amount of Rainwater You Can Collect From Your Roof

Rainwater collected from the roof of your house, agricultural building, office block, restaurant, manufacturing, or industrial building can be the capture area to provide high-quality water for reuse.  The volume which can be harvested can be substantial over the course of a year and here we run over how you can make the most of the water you can save.

1. Investigate the average rainfall where you live

You need to know how much rain falls in your area, as there can be big variances from locations on the east side of the UK to the west. The Met Office can provide you with an accurate rainfall of your area here.

2. Calculate the surface area you can collect from

Rainwater is generally collected from the roof so working out the capture area of the roof is a good place to start. Multiply the length in metres by width for roofs which will give a square metre area of your roof in square metres. Roof area (footprint) in square metres x annual rainfall in cubic metres.

3. How much water can I save?

To work out how much rainwater can be harvested, multiply the average rainfall (mm) for your local area by the roof surface area (m2).   This number will give you the number of litres of water you can expect to collect.

(650ml = 0.65m3), divided by 12 = average monthly rainfall capture.

e.g., 450m2 x 750ml = 337.5 (m3), divided by 12 = 28.125m3 or 28,125 litres per month average.


Use the above formula for an initial calculation – our online calculator is here

What Size Wate Tanks are available?

Rainwater harvesting tanks are available for above and below ground installations, single moulded water tanks are avowable up to 30,000 litres with linking kits to store up to 120,000 litres, and underground tanks up to 9500 litres. This water can be used for agricultural sprayers off a grain store, water for dairy wash down from barns, pressure washers, greywater systems for flushing toilets for commercial factories and office blocks and several applications for washing and cooling. Rainwater filters are available for removing leaves and moss out of the water coming off the roof to save a build-up of sediment in the tanks.

Rainwater Site Visits & Installers

Enduramaxx work with several installers around the UK who can carry out site visits and water use and savings audits for systems. In short, we can work with you to develop a rainwater harvesting system that will work for you.

Get in Touch - Find Out More

Visit Our Blog

Related Posts

Calculating Your Roof Surface Area for Rainwater Harvesting

Calculating Your Roof Surface Area for Rainwater Harvesting, your roof collection area, when you...

Calculating Your Roof Surface Area for Rain Harvesting: How Much Can I Save?

Calculating Your Roof Surface Area for Rain Harvesting – Your roof surface area is the size of your...

How to collect rainwater for your garden | Enduramaxx - Manufacturers of Polyethylene Tanks

How to collect rainwater for your garden, rainwater can be collected from roofs and greenhouses,...