I just think we have gone way overkill on this issue.
WanderingDaisy, your points are well taken, your career credentials are admirable, and I appreciate your input. What I have personally found is that strange bugs in water I'm not use to are the ones that make me sick. Perhaps we build up an immunity over time to the bugs in our own water supply, whether it be our own backyard well, our local city or municipal water supply, or even the rivers, lakes, and streams in our immediate area that feed these same wells etc...
I could not drink the tap water flowing up from the volcanic lakes under ground when I first moved here four years ago. I would get stomach cramps with every attempt. Now, after living here these four years, it no longer bothers me. However, if I go to the coastal areas and drink water from the underground volcanic lakes, I get worse stomach cramps than I did here. If I stay a month or so there, and continue to drink the water, the stomach cramps begin to subside with no medical treatment administered.
The locals all swear this village water is good, they use it without filtration or other treatment, and appear to have no visible health problems with it. The villagers 20 miles across the lake say this water in my village is bad, and won't touch it, but drink their own, and visa versa. When we go over there we bring or buy bottled water and they do the same while visiting here. Mexican nationals from around the country will drink their own local water back home, but will not drink any other Mexican water when on vacation away from their own areas. They will even stock up on their local bottled water to carry with them.
So, I guess you're safe drinking your local water as you describe, but I would not be guaranteed to handle it as well while just visiting there. Nor would you do well drinking my water when you first get here. My water filter, chemicals, and UV treatment, protect me when I'm away from the water supply I have adapted to or built up an immunity to.
A good example of just how well water filtration and UV treatment works is the case in which tens of thousands of lives are being saved in the African nations even as I write this. Without water filtration the people of the third world nations are dieing every hour from dehydration, brought on by diarrhea, brought on by drinking unfiltered disease and germ ridden water. The proof of "how do you know it works" is in the well publicized successful results of filtration and UV treatment use taking place in third world countries. Sometimes we just have to trust professional test results as published. Just like you trust that your computerized ABS brakes, that someone designed, built, and promoted as being trustworthy, will not to lock up on those mountain curves.
Be grateful that you have a clean water supply, and lend a hand here in adding to the knowledge base that could, potentially, be used to save lives on a global scale. There are a lot of bright, dedicated, well educated people with an amazing amount of common sense on this forum, please don't dampen their enthusiasm. This very important subject has not even begun to enter the realm of "over kill". Peace, Brum