Neil it is likely as your in Edinburgh you'll have very soft water. Where in the Edinburgh area do you live. I'd think a HMa unit would be all you'd need. Cheaper in the end than tap water or a Ro unit. you also don't have to add any chemicals or minerals. all you do with the water that you produce is either stait in to the tank or store in water butt, heat and keep the water circulating by either air line or powerhead. Check RO man site for some good deals