Meet the new water toxins, same as the old water toxins
Assuming it doesn't get cockblocked by industry or shut down by Michele Bachmann, the EPA is going to start regulating some gross stuff that hangs out in your water — not because these are new toxins, but because they're finally being allowed to do something about the old ones. Forbes has a rundown on what you've been drinking, and how to stop drinking it anymore.
Perchlorate: It's an ingredient in rocket fuel! Yum. Under the Bush administration, the EPA decided not to regulate it, but the Government Accountability Office cast doubt [PDF] on the validity of that decision (because the scientific method was atypical, i.e. something fishy was going on, and also because hello, rocket fuel). Now the agency has reversed its position. You can reduce perchlorate with a reverse osmosis treatment system, which is super expensive, so maybe just wait for the regs to kick in. After all, you've already been drinking it all your life.
Hexavalent chromium: Chromium in general is regulated, but this is the worst (i.e. most carcinogenic) kind of chromium — and if you live downriver of a steel mill, you may be getting unhealthy doses. You can get this one out by distilling or filtering your water, but a typical kitchen filtration system like a Brita won't do it. Or if you shelled out for that reverse osmosis thing, you're golden.
Volatile organic compounds: If the word "volatile" next to the word "organic" conjures up images of a chestburster from Alien, you're not far off. VOCs are carcinogenic compounds that come from extremely non-drinkable sources like industrial solvents. Eight are already regulated, but another eight will be joining them in … oh, you know, two years or so. The ship of getting carcinogenic crap out of your water turns slowly. In the meantime, the reverse osmosis system, it does nossing! But carbon filtration will do it.