î live just down the road from you in Shropshire and we also have chalky hard water.
You will get some strange advice from overseas APUGgers about distilled water. It seems much easier to obtain in other countries. At one time a still (since it can be used to distil alcohol) had to be licenced . I think that is still the law today in the UK - it maybe makes distilation an inconvenient and more expensive process, but I think there may be other reasons. Distilled water should be water that is distilled - can,t be anything else, yet I,m not so sure that is the case everywhere. There is also de.ionised water and de.mineralised water, but I suspect the terms are sometimes used interchangeably in countries with less pedantic labelling laws.
The big curse in the UK is that supermarkets decided they could charge more money for the water for steam irons if they stuck perfume and colouring in the stuff :-(
About the only place you'll find it now, at prices lower than Halfords, is if you find a proper old car repair garage out in the sticks somewhere. I found one the other week in South Wales. £1 a litre bottle for demin. I bought as much as I could carry.
But yes... I only use for the very final rinse with photoflo and when mixing my own developers. A few litres will last me a long time.