Posted: 22/06/2016 at 17:09
There's a simple answer to that Pete8.......some of us go to fill up the can from the butt, spot something else which needs doing and forget to keep an eye on the can
To be a little more serious, it is a good idea to fit water butts on any house / GH / outbuilding where possible. Piping overflows to keep a pond topped up is something I do too.
If you find that your butts overflow, a diverter kit will allow you to run the excess off into the main drain.
Most plants would prefer rain water and as Ladybird says, if your water is metered, it saves a few pennies.