Whats it for anyway? Mixing or something. I think this is another one of the tattoo people pussy footing about with stuff, making out that those who are new to tattooing are somehow doing it wrong by using tap water, while all the time secretly that is exactly what they use!
If you can wash any wound with tap water, or drink it, its not that harmful is it.
If you asked a so called pro tattooist if he wanted to buy some distilled water, what do you think he would say? Ey, that could be the next game..... In a few words, what would the tattooist say under his breath whilst handing over the money.
distilled water by the way can be bought at Biostain in Manchester off the shelf. I think they have got an ebay shop.