At this time of year with spring runoff, tap water has a certain grittiness combined with extra chlorination makes it almost undrinkable.  Just because tap water is safe doesn't mean it necessarily tastes good.  If coffee or tea was served at your local Timmies or Starbucks tasted that bad you would send it back.

People with sensitivities to chlorination makes it uncomfortable.to drink as it makes the inside of the mouth burn.