I don't yet want to replace my existing cylinder yet but I do want to be prepared with a product when the present cylinder inevitably leaks. I have an existing Vulcan continental boiler that I wish to continue using (until it wear out after which time it will probably be a condensing boiler) and I have a very powerful power shower with 4 body jets manufactured by Aquilisa which empties all the hot water in under 5 minutes, and a theoretical emptying of my 50 gallon roof storage tank in under 12 minutes given half a chance. This high flow rate ensures that instant domestic water heaters would be inadequate. My copper cylinder has an electrical immersion heater, which I would like to preserve as an insurance policy against boiler failure. Here in lincolnshire we have got the hardest water in the country. Obviously the new copper cylinder replacement will be a larger volume and be ready lagged but has anyone got any ideas on replacement hot water storage devices that are hard water tolerant and can incorporate electrical heaters for fitting in an airing cupboard? Links to websites would be appreciated.