collecting rain water off the roof

[aquilegia]

Maths isn't really my strong point - how do I calculate the amount of rain water I'd collect off the roof? I'd love to use it on the garden, rather than just letting it go down the drain.

Is it practical? How many butts would I need?

[aquilegia]

[kenkew]

Lots of 'If's' and Butts' here.
Depends on the size of your roof and the rainfall in your part of the world. ie; If you get x" of rain in a 12 sq" container over X days, then multiply this into the sq" area of your roof. That will give you x" depth of rain. (There is 1 (UK) fluid oz per 1.734 cubic inch -or- 1 UK gallon to 0.005 cubic metre.)
Now, doesn't that make you feel better?

[aquilegia]

better - probably. Confused - definitely. I think I understand. Must measure the house when I get home and get my calculator out for much head scratching...

[kenkew]

To be honest, your best bet is to buy one of those fall-pipe kits which catch your rainwater and divert it into your barrel. When the barrel's full, the connection to your water butt is shut off and the rest of the rainwater flows down the fall-pipe to the drain as before. If you have room you can add more barrels connected to the first one.

[kenkew]

.....which raises another question. After quite a bit of fiddling and bodging I connected two butts together. The pair on the plot I connected at the base with a base fitted outlet. This gives me maximum quantity from one tap on one butt but the seals had to be strong enough to hold the pressure. At home I did the same but connected them together at the top. This means having a tap fitted to each butt. Has anyone any tips on setting either sort of connection?

[aquilegia]

thanks Ken - I like that idea. Sounds far less mathsy!

[Hugh_Jones]

Aquilegia, a very simple calculation:-
Multiply the length in feet by the breadth in feet and divide by 12 - this gives you the number of cubic feet for each inch of rainfall.  Multiply this figure by 6.24 (the number of cubic feet in a gallon) gives you the total number of gallons per inch of rainfall.

The answer to ken`s question is equally simply.  Connect the two butts with a hosepipe syphon tube, making sure the ends of the tube reach the bottoms of both butts. Whichever butt you draw from the levels will remain equal in both butts.