I think some of the companies are using an additive to the plastic to inhibit microbial growth. I don't know if it's microban, but it is something like it.
If you run the water through a filtering system it will pull out the chlorine and when you put it into your not clean bladder, the microbes go nuts. Doesn't take long to get slimy, get cloudy or show spots. The big problem is that unless you use a 10% bleach solution or something like that, you really can't get them CLEAN.
Kind of like brewing, I think.
The water itself is not attacking the plastic. Even DI water doesn't have an effect on plastics.