With Rain Water Being Harvested For Watering Gardens, Harvesting Rainwater Is One Of The Most Popular Eco-Interventions Taken by British Households.
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Figures are hard to come by as there is no UK legislation covering the fitting of water butts to domestic properties. But it seems like as many as 7-9 million UK homes use water butts on their downpipes. And as the threat of intensive rainfall increases the fitting of “Smart” water butts could accelerate. More on them below.
How Much Water Is Stored In Water Butts Each Year?
Large water butts average 200 litres but they come in various sizes as shown in the table below. Add to that list IBC tanks which are 1000 litres and obviously calculating the UK storage potential is near impossible.
And many people have more than one water butt. In my own garden I have several 200-250 tanks stood right next to downpipes and these “overflow” to a couple of 100 litre IBC tanks that are screened off in the garden, plus some smaller tanks and a dipping tank. In total I can store around 3000 litres.
But 3000 litres can soon be used on a large garden or greenhouse. So how can we maximise the total amount of water that can be harvested? More on that in the next section.
Standard Water Butt Sizes
Capacity (Litres)
Best For
Typical Dimensions (approx.)
100L – 150L (Slimline / Space-saving)
Small patios, balconies, greenhouses, or houses with tiny courtyards. Great if you only have a few potted plants.
Height: 90–100 cm Width: 35–40 cm
200L – 250L (The Standard)
The average UK suburban garden. Perfect for watering a medium lawn, flower beds, and a few vegetable patches.
Height: 120 cm Width: 60 cm
300L – 350L (Large Domestic)
Keen gardeners, small allotments, or larger properties with high water demands (e.g., lots of home-grown vegetables).
Height: 130–150 cm Width: 65–80 cm
500L – 800L+ (Commercial / Multi-tank)
Large allotments, smallholdings, or properties looking to maximize water independence. Often achieved by linking multiple 200L barrels together.
Varies (often wide tanks or interconnected units)
Maximising Harvesting Capacity
There is a limit to the amount of water we can store. In some gardens this is just 100-200 litres and in mine it is 3000 litres. In both cases once those tanks are full any extra rain runs to waste. But once we start to use the water we release more storage capacity and it is how we use this that is the key for me. Though we often get long dry spells we also get the occasional shower. It might only be one mm of rain. But that can go a long way if we plan ahead.
The thing is one mm of rain fall on a square meter is one litre of water. And that means if we are collecting from a 100 sq metre roof we can fill a 100 litre tank in just a few minutes! This might sound like magic but it reality.
What is also reality is that most homes only collect rainwater from a fraction of their roof space. They have a water butt next to a single downpipe. Or perhaps they are more adventurous and collect from a couple of downpipes. And that means that several downpipes are sending rainwater to the drains.
The secret to Maximising Domestic Rainfall Harvesting is to harvest from EVERY downpipe.
How Maximising Domestic Rainfall Harvesting Works
Many people think that a water butt looks ugly, takes up too much space or have other reasons for not harvesting from every downpipe. I understand that. I don’t want a water butt attached to all my own downpipes.
But it isn’t an issue.
I have water diverters on every downpipe and run pipes from them to water butts and strategically screened IBC tanks around the garden. the diverters and pipes are small and barely noticeable. And the hosepipes I run to the storage tanks are either at the backs of borders and unseen, OR buried underground. A few inches deep is all that I bury them. Freezing isn’t an issue as in frozen weather there is no amount of water running through them. And in winter the tanks are already filled from autumn rains.
My roof area is just over 150 sq metres. So a mm of rain, which is very little, gives me 150 litres (33 gallons) of harvested rainwater.
In the last 24 hours, (up to noon own May 18th 2026) we had approx 8 mm of rain where I live. That means I harvested 8×150 litres. 1200 litres in one 24 hour period in May .. not bad.
It is enough to fill an IBC tank and have some left over!
So my message is that the secret to Maximising Domestic Rainfall Harvesting is to harvest from every downpipe.
