This is a very interesting question and a definitive answer may not be easy to come by, depending on what is important to you. A closer look illuminates yet another challenge in how we view water. To begin, whether we drink well water or surface water it all comes from rain, without exception. However, what path the water takes makes all the difference in the world as to whether it is good or not to drink.
Case 1 – It Rains, you hold out a glass or open your mouth and drink. Remember that water is aggressive to absorb contaminants from the atmosphere so if the rain you drink passed a lot of pollution on its way down to you, then it brought some contaminants with it. If you are in extremely high elevations rainwater is likely to be less contaminated than that of heavily industrialized, concentrated cities. Rainwater is not potable water.
Case 2 – The rain fills your well or aquifer. Again, water is aggressive to absorb contaminants so if the ground has contaminants in it, so too will your well water. By itself, well water is not necessarily potable water.
Case 4 – You drink from a municipal water supply. It all came from rain-water but of course, is filtered and treated with chlorine and perhaps fluoride. You might not like these chemicals but municipal water is potable and considered safe by the EPA.
Case 5 – You drink bottled water. It originates from rainwater. but is also filtered and has minerals added to it for taste. It is potable, safe, and expensive.