If you live in a hard water area, like me in Kent, then pure water is great for steam irons. I have a long standing customer who has a few litres each time I visit. I use it in ours and our steam iron has lasted years, which it wouldn't otherwise down here, our tap water 450ppm and very chalky.
Tescos sell ironing water with a bit of smelly stuff in it for about a pound a litre, did think of selling it but never found the time