Well I only commented because I wanted to use the word "Enforcer" or maybe "Regulator" like an old timey government gun slinger :-)!
But yes, things do fall between the cracks and even if they didn't it's often hard to enforce/regulate illegal activity by big corporations in a large scale way. It can be done but court action and injunctions, etc... take time, regulations change mid way, and changes are slow to happen. Water was probably never safe to drink (think of all those millions of herds of buffalo and other animals doing what they do when nature calls) all that stuff goes down river and the methane goes into the air. But industrial pollutants (my forte) has become a huge problem. It's much better then it was back in the 60's and 70's and 80's but I don't think you'll ever be able to put a complete halt to it. Too many people (also doing what they do when nature calls), watering their fertilized lawns, draining their chlorinated pools, washing their various cleaning chemicals and prescription drugs urine, their food wastes, etc... into the sewer system, The list goes on and on and on. Add to that too much industry and their wastes, agriculture and livestock production and it's wastes, and not enough fresh water supplies or treatment plants, and ..well... here we are. Like I said, it IS much better then it was thanks to more regulations, but it'll never be great.