I know first hand how hard the water companies are working to reduce leaks and they plough Millions of pounds into improving their performance. If they don't hit the targets imposed on them by OFWAT they are fined. Gas and electric companies don't have the same problems, as they can make or buy more product, no matter how many new thousands of houses are built.
Always check your local water companies web site for advise.
I now have 3 water butts and will be buying 2 more this year, Im also very grateful for the advise for drought tollerant plants. Think I'm going to invest in more grasses.