Bill, please keep your pleas out of the News and Rumors Board. If you would like to persuade others to accept your vast wealth of knowledge regarding the functioning of the parks, utilize your PM button. Being banned from wdwmagic once is more than enough to ruin any of your credibility, as it is pretty hard to get banned from wdwmagic...
Regardless, E. coli is a bacterium, and it would take a very fine filter to get it out of the water, one which I doubt Disney ever invested the money to buy as it would require constant replacement and is quite expensive--we use dime sized filters in my chem lab, and they aren't cheap, I could not imagine what would be needed for filtering bacteria out of Disney's water. The other option would be to have giant water filters that douse the water in bleach and then filter the bleach back out so as to not kill park guests. It would be prohibitively expensive, and if such a filter were in use, I don't see why Disney wouldn't have spent the extra few bucks to have a heater so the water at River Country weren't 60º in the winter. So it makes sense to just have water parks filled with normal pool water that can be chlorinated to kill everything we don't want on our bodies. Yes, there are races across the lake, but you sign a waiver for that, because there is always a chance of getting sick, just like there is swimming in any lake. That is why you don't see any companies opening up lakes for people to swim in while guaranteeing their safety. While the odds of infection are low in waterways populated with few people, if you have a few thousand people in there a day, all mixing their own bacteria in with the resident microbes, it becomes a lawsuit waiting to happen. Why risk it when Blizzard Beach and Typhoon Lagoon are far more popular and accessible?