It’s reasonable that you trust them.
You did not quote them saying that there are not prescription medications in the drinking water supply. You quoted them saying “it’s fine and safe and nothing to worry about.”
While it’s your prerogative to accept that at face value, I think it’s worth knowing if prescription drugs are in the drinking water supply.
Furthermore, if you want to win people over to “your side” you need to actually break down and prove people you disagree with wrong with hard evidence as opposed to dismissing their claims out of hand.