Do you want 'clean' water to stop limescale or for health reasons?
Are you bothered by limescale in your washing machine/dishwasher too?
If you're doing it mainly for health reasons then I recommend getting a distiller. This gets rid of all contaminants, whereas I don't think the reverse osmosis ones do. Nor do tap filters.
Distillers start from about £70 for a plain white one or about £120 for a nice black/silver one with a glass collection bottle. Both work exactly the same. They will cost you a few quid per month to use. I think they're about 500W and need to run for about 4 hours to produce 4 litres of water, so they use about 2kWhrs per day which is about 40p.
Then get yourself a cheap shower in-line filter (about £10) to filter out chlorine and heavy metals. You can also get an in-line filter to place before it reaches any appliances. I'm not sure on price of those but they will remove chlorine and limescale too.
EDIT:- The distiller will produce nearly pure water and as such it should really be re-mineralised. I use omica superionic fulvic minerals - just a couple of drops into each glass you drink will provide a nice balance and improve the taste (distilled water can be a bit sharp due to carbon dissoliving from CO2 in the air). Or you could use ReLyte or ReMag or similar things.
This message was last edited by fazarelli on 14/05/2016.