Well water brings a different set of problems.
Well water is basically water in its natural state, and so can be affected by a huge variety of issues, depending on location, depth, geology, soil, etc.
Some common issues however are:
- high iron content
- bad odor
- high solids content
- presence of bacteria, lead, cysts, radon, arsenic, nitrates, metals and other health-affecting materials
Hygienic testing needs to be done every few years, and even more often on problem water sources with a history of issues.