Hi there
On the topic of well water, it would depend on what is in your specific well. I know my well gives us a lot os sulfur and iron both, making plant growing a little difficult. In all likely-hood, if you can drink it your fish will be fine. It would be wise to check it for the three dangerous nitrogen compounds (nitrate, nitrite and ammonia) just to be sure. Also if you use a water softener it might be a good idea to use half water from you tap and half from a hose or other source that is not softened.
City water through a python, if left untreated for chlorine or chloramine, would harm your fish, yes. However as long as you treat the tank for the amount of water you are adding either before or at the same time you add it, the short exposure to the chlorine/chloramine would do negligible damage and is not of much concern.
Hope that helps