Been posted at this price loads of times - I know because I've bought before

​Add Iron and then drink.

Distilled or deionized water is commonly used to top up the lead-acid batteries used in cars and trucks and for other applications. The presence of foreign ions commonly found in tap water will drastically shorten the lifespan of a lead-acid battery. ... Purified water is used in freshwater and marine aquariums.

Just bought 5ltr from Halfords for £3.50 the other day!! :-(

I use it for custom watercooling on overclocked computers :-)

Nope. Unless your kettle collects the water and condenses into a sterile container, I'd argue that water from the tap has less impurties then boiled water, your just wearing you battery out quicker by even putting anything of the sort in, just spent £1.60 and get stuff that's already gone through the process.