What size of water butt do I buy?

dharm999

Am going to replace two apex sheds, with two pent sheds, one is 10 x 8 and the other is 16 x 8.  Am planning on putting guttering on them do I can collect water in a butt.  Having never had one before I have no idea what size I need?  Given the size of the sheds, are 100 litre and 210 litre water butts too small in proportion to the shed roofs?  I’m going to have the gutter down pipes directly go in to the butts, so need to think about overflow and having a soak away under the butts.  I’m in Scotland, east coast, so it can be wet. 

Thanks 

QrizB

In the UK, in round numbers, a square metre of roof will catch about 1000 litres of rain a year, 80 litres a month, on average. More if you're north and west, less if you're south and east.

Your 10x8 shed is 7.4 square metres. Your 16x8 shed is 11.9 square metres. You might expect to catch 600 litres and 950 litres a month, respectively.

The missing part of the equation is how much water you're expecting to use from the butts. If you only need 200 litres a month there's not a lot of point spending too much on butts.

However I'd probably put a single 200 litre butt on the 10x8 and two of them on the 16x8. You'll be able to refill them almost every month.

I wouldn't bother buying 100 litre butts; the cost saving is small, the amount of work to fit one is the same. The only reason I can think of is if you're really tight on space.

Edit to add: see rainfall map below.

1000mm of annual rainfall (where the brown turns into white) is 1000 litres per square metre per year.

800mm is 800 litres a year, 1250 is 1250 and so on.

Brie

check to see if your water company has any deals on them.  the one where I am sells them cheaper than the shops and gives you the first 1 free.  Very MSE.  

molerat

On my butt set up, 2 x 210 litre butts linked at the base because they are one in front of the other in a narrow gap, I fitted an overflow with 3/4" hose running to the drain.  It seems able to take the water from the 8 sq m collection area when the butt is full without too much overspill. 

Slinky

We have a large and a small waterbutt connected together, collecting water off our garage roof. It's actually all the water off of our double length and our neighbour's double length garages, so the equivalent of 4 single garages. We're in one of the driest parts of the country, but even so with all that roof space to catch, sometimes we run them dry in the summer. I'd say get the biggest butt you can.

dharm999

Brie said:

check to see if your water company has any deals on them.  the one where I am sells them cheaper than the shops and gives you the first 1 free.  Very MSE.  

Thanks, checked the Scottish Water site and they aren’t doing anything in my area

dharm999

Thanks to all that commented, the consensus seems to be that 1 200 litre butt for the small shed and 2 butts for the bigger one.

subjecttocontract

We bought one of those 1 cubic meter (220 gallons) plastic containers. Most years its full by early spring and it runs out just at the end of summer. We're glad we didnt buy a smaller one. That's what I'd recommend. You can never have enough rainwater available......a long hot summer and it will be needed.