HCl itself isn't going to be a direct issue in the water supply. HCl interaction with all those other things in the environment that were otherwise inert is the big problem here. If you dump your HCl in a limestone environment, we'll you'll dissolve a bunch of rocks. It gets more problematic when there heavy metal compounds get dissolved into solution and suddenly people can't use their wells or municipal water has to shut down or work extra hard at filtration.

Problem is the only way you know if this is occurring is constant sampling and testing over the affected region by a competent and trustworthy set of testing groups.