Yeah, you're going nuts over the water thing (just like I did). I also use Brita though I don't think it significantly reduces anyone's chances of blc (or any other kind) - unless you live in China downstream of some factory spewing carcinogens into your drinking water.
If you want really clean water, use distilled. You can buy it in plastic bottles, but then you may worry about those pesky plasticizers (sp?). So you can do what a friend of mine did, which was to install (he bought it) a water distillation unit, so he had really great water. But then you gotta be careful because really pure water can leach metal out of the metal tubing. You can store it in special plastic containers (HDPE), basically really hard plastic. The plastics companies will tell you that you've got nothing to worry about - they might be right.
The concern about distilled water not being safe to drink urban myth (IMHO). It originates from the fact that you can place living cells in distilled water and due to osmotic diffusion, the cells will expand. Similarly, place those same cells in very salty water and they will shrink. But keep in mind that the moment you drink distilled water and it enters your intestinal tract, it is no longer distilled, it becomes, well, rather nasty.
I'd be (and am) comfortable with a Brita-like filtration system. RO (reverse osmossis) would another step toward purer water, but I'm too lazy/cheap to invest.