I have been reading on the internet about people buying distilled water and saying never use tap water. The only reasons I can find is that if your area has hard water, a softening agent will be added to the water. Also there can be added clorine that is bad.
I think in BC we have soft water. So I guess there are no softening agents in my tap water.
Personally I have a system of filling a big rubbermaid tub (around 100L) with tap water through a hose. I leave it uncovered for 2 or 3 days. I stir it daily to release bubbles that collect on the sides of the tub. I figure that I am letting out the clorine gas and any other bad additives.
How are other people dealing with their water supply? I guess I should add that I am using pots with soil to grow.