it all depends on the properties of the water, you need to test for nitrite, nitrate, ammonia, hardness, ph these are the common test that you would need to carry out to assess the suitability of the water
When I moved into my new home, I was forced to use well water because at the time that's all that was available. I discussed it with a LFS whom I trusted, they recommended I use an ammonia and chlorine remover just to to be on the safe side. I must say I was pretty nervous about it but, I tried what they suggested and didn’t encounter any repercussions. One other thing I would like to mention, I used well water with and without a water softener.
I currently am weening a "test subject" Betta from tap to well water. I am doing it slowly because the pH is quite different! I have tested for pH, Ammonia, Nitrite, Nitrate, GH, KH, Phosphates, and Iron, and all have come out fine. The tap water around here is around 7.7 pH with over 5 dKH, while my well water is pH of about 6.0 with less than 1dKH.
I wouldn't inject CO2 into this water without buffering, but I think Rams, Apistos, and Betta's will like it just fine!