I found that the chemist sells purified water (£4/5 litres), which is not actually distilled water, but close enough for me. The purification method includes reverse osmosis and that's a good way to remove fluoride. I actually doubt if fluoride or chlorine were ever in the source water. So I'm using purified water for DMSO due to the chlorine/fluoride risks with the BBB. For oral H2O2 (Hydrogen-Peroxid) I'm sticking with tap water that has been left standing to allow some chlorine to dissipate (it dissipates faster when warmer, ie out of the fridge but cool not warm, and lightly covered).