Why is water is tasteless?

Answer 1

It is not tasteless. It tastes like water.

Answer 2

Well ... it's not quite "tasteless" but it sure comes close.

Pure (distilled) and pH neutral water is pretty much without taste -

because it is not salty, sweet, acid nor base - and it has no smell since it is the solvent which your body uses to dissolve the molecules that you cal smell.

(And people do complain that it's "tasteless" )

Most of the water we drink has metallic (ions) impurities which gives water a very mild taste.