Your mouth can tell you when you need to drink water, but not how safe it is. For example, arsenic and bacteria—two big drinking-water threats—have no noticeable taste. Lead has a mild flavor and can even be sweet.
A metallic flavor can signal low (safe) levels of metals. And though chlorine tastes bad, it keeps water clean. But, if tap water suddenly changes flavor or appearance, that could mean problems, as folks in Flint, MI, learned the hard way.