[Gary] A reverse osmosis (RO) system is an excellent system to remove most contaminants.  But you must soften the water with a water softener if you use RO.  This applies to both city and well water.  And all water needs to be free of coliform bacteria.  If you need to remove that then you should use ultraviolet light filter and I would recommend a professional install that.  All city water systems are supposed to be coliform free.  If a private well has coliform you should try to rectify why it does and if you can’t then use ultraviolet light filter.  Hope this helps.

[Andrea] Another note about water softening…some systems need iron filtering. We have a bit of iron in our well, but not enough to necessitate that. We do bleach our well about once a year, though, and that takes care of any bacteria.

Putting it all in order: From the well, the water goes to a whole-house sediment filter, which gets rusty and is changed out every 2 months. Then comes the softener, then a whole-house charcoal filter (changed every 6 months). Then for drinking water we have an RO system.

Each water filtration system needs to be based on your water source, quality, and contaminants.