I'd refer them to the studies of the uber expensive bottled waters that so many buy. Besides what is finally coming about the chemicals that leach into it from the plastic bottles, most of bottled waters are merely recycled tap water from our major cities, like LA, Denver and Jacksonville. Both Disani and Aquafina are from those city taps. Add to that, a lot of those cities drinking water is recycled from waste water - sewage - and still contains high levels of prescription drugs, birth control pills, etc.
I'll take my well water any day.
hint - if you DO use bottled water, look for the source of the water. If it doesn't say "spring water' it's city tap water. Funny part is, spring water is much cheaper.