Chris, the only answer is to try it and see, after all, thousands of french and Spanish drink it every day, and suffer no ill effects, and we have never had a problem with the water whilst there on holiday.
A Brita jug will NOT filter out harmful bacteria , if they are present.
If you have any doubt, either boil the water, or use bottled water(which may or may not be worse than tap water)
I think the problem with water and stomach upset is not that there is anything wrong with the water, it's just that you're not used to it. When I visit friends in Africa I get stomach upset, but when they come to England they get it