Actually, most municipal water departments use chlorine dioxide, not sodium hypochlorite (chlorine bleach), which, I've been told, can leave some nasty compounds behind it.

My-daughter-the-veterinarian told me that to prevent leptospirosis, I should keep my dog out of stagnant ponds or small lakes that have no outlet, especially when cattle are present, and treat his water from such sources. This is a good rule for humans, too! There is a canine vaccine for leptospirosis, but it often causes severe reactions and, per the University of California at Davis School of Veterinary Medicine is not very effective. My dog is actually owned by Canine Companions for Independence, even though he was rejected as an assistance dog, and they do not allow their dogs to get the lepto vaccine.

I would assume that the same rules apply to humans. If you're in cattle country, take along some chlorine dioxide tablets (I take some anyway in case something happens to my filter), and resist swimming in lakes with no outlet. The filter will take care of the protozoa that chemical treatment takes 4 hours to zap, so you only need 20-30 minutes' chemical treatment to kill bacteria and viruses.

I did a little googling but couldn't find out if lepto bacteria are of a size that most filters will remove. Thanks for finding this out!