Water quality issues are something I have dealt with to a small degree professionally. I have seen people drinking from water sources that I would not want to touch despite them appearing healthy, so I assume people can become conditioned over time to at least some water born illnesses, like high coliform bacteria counts. We used to take samples regularly as an independent party for one of our local banks and also real estate agents, then sending the samples to labs. Often water sources such as springs and shallow wells would test positive for coliform bacteria. From what I have been told this is from decaying vegetation and is not harmful. Sometime we'd get samples identified by the labs as fecal coliform, which is usually from rodent feces and is not OK. Ecoli also showed up once in a while with a shallow well or spring and this is very bad. Any coliform count can be taken as an indication that a water source could be compromised. Around here a lot of the mountain streams are probably OK to drink from based on personal experience and the word of one of our local docs. However, I have heard of people getting "Beaver Fever"/ giardia from some of the irrigation ditches that have had more time to run through cow pastures. In fact I have heard that our local lake which is fed from high mountain streams in some cases originating from small glaciers has been found to contain giardia. Many people take their water directly out of the lake, so unless they have a UV or reverse osmosis system are rolling dice. A local town uses it as it's main supply, but with appropriate filtering. As to railroad water tanks, I think to be safe you'd need to be assured that the source was safe and second that the tank itself could not be contaminated with rodents, or dead bats like Jim Grigsby mentioned. The water out of the well that supplies our McEwen tank might be drinkable before going into the tank, but not afterward.
