Water is a tricky question. I have a well so I use a heavy duty carbon block filter with a UV light that filters at the kitchen tap (installed under the sink) and that does the job very well. This is what I've used for over 20 years. Makes the best kombucha by the way
For folks on city water with fluoride, I would recommend spring water in glass jugs. This is because filters that claim to take out fluoride don't do a very good job of it and a lot of the fluoride still remains after filtering.