I was in the south pacific in the early 1990's and was without running water or power for five weeks after a massive typhoon. I was lucky enough to have a First Need Deluxe with me and I never got sick. I drank from dirty swimming pools and tree stumps. Where ever I could.

I now own a Steripen and it works just fine too. Different usages. The Steripen is good for water that is clear with the threat of live organisms. Most backpacking and all drinking in foreign countries are just fine.

First Needs are good for when you have mud and leaves and runoff in a swimming pool.

That being said its hard to know if you would want to drink any standing water in a disaster area like say Katrina that could have oil or toxins in it above acceptable levels.