Water systems receive untreated water from whatever souce avaiable and proceed to prepare it for human consumption. This generally involves filtering to remove solids present in the water (usually by decantation) and some anti-bacterial treatment (usually by addition of chlorine). After that, water must be carried until it reaches the tap.

Some problems that could affect the potability of such waters are:
1. Water that is particularly polluted at the origin - too much sediment, too much metals, too much organic matter, etc . . .
2. Water that is not correctly treated - application of less chlorine than indicated for budgetary reasons (or even not chlorination)
3. Tubulation that distributes the water (carries the water from treatment station to point of consumption) is too old (oxidation) or has infiltration from the sewage system, etc . . .

As you can see, not all water is fit to drink. But it must be evaluated from city to city, sometimes from neighborhood to neighborhood.

And this has nothing to do with mineralization or the taste of water.