[qinsig]

Pollutants don't get in because water pipes are pressurized

[SkyPuncher]

Absolutely not true. Pollutants don’t get into the lines because there are decades of mineral deposits built up inside these pipes.

[djtriptych]

isn't this only true if they are always pressurized?

[frosted-flakes]

They are always pressurised during normal use. When they are depressurised because of a water main break or for maintenance (and they try to do this as little as possible), orders are given to flush the lines before drinking any of the water.