I want to know what word should I use to describe the taste of water. I always say it tastes nothing to mean that it does not have taste, not sweet, not salty, not spicy, and not sour.
The researchers identified what they call the "three main tastes of water" that can be found if one swigs a great variety of bottled and tap waters. These are "the bitterness of poor mineralised water, the neutral taste (associated with coolness) of water with medium mineralisation and the saltiness and astringency of highly mineralised water."
Water tastes like whatever minerals or flavorings are dissolved in it. It might taste metallic, or fruity. It might even, metaphorically, taste like a brand new day. When there is salt in it, it triggers those taste buds that respond to salt, and thus it tastes salty. Absent anything else, and simply as a function of the perfect blending of some H and some O, water does not trigger taste buds as far as I know. But I guess one could say it "is refreshing."
There are understood to be five basic taste sensations: sweet, salty, bitter, sour, and umami. Languages differ in whether they have individual words for each of these sensations. The English word savory, for example, could refer to both salty and umami. Many African languages have a word which is usually translated as "sweet", but which can refer to salty, sweet, and umami flavor. One Yoruba proverb, translated as
...a mouth as sweet as salt
refers to somebody who is very gifted in persuasion. Languages also differ in the extent to which they have words used for describing food textures.
As for flavors which can't be easily classified as falling into one of the five main categories, there is much more variability in the kinds of words which can be found in a language. Referring to the sensation of drinking water would fall outside of the taste vocabulary. You could use a word like watery to describe the mouthfeel, or cool or refreshing to describe its effect on the body.
Water tastes tasteless. Wet is more of a description that is related to feeling or using the sense of touch or touching. Scientifically, plain water is either of neutral taste or tasteless because it is impossible to burn water and the bitter taste only manifests itself when something is or was burned.
From a purely linguistic standpoint, surely if salt tastes salty then water tastes watery, right?
A lot of the answers seem to presume that water tastes of nothing, or indeed must taste of nothing. That isn’t a linguistic question but a biological one, and its answer isn’t quite as straightforward.
All water that you buy or get from a tap contains a cocktail of various minerals which all modify its taste. Most carbonated mineral waters for instance are slightly sour (simply because the chemical which makes it bubbly, carbonic acid, is sour) but also salty, bitter or sweet, depending on which minerals in it dominate.
Almost pure H2O doesn’t taste of a lot because neither our taste receptors (on the tongue) nor our smell receptors react strongly with the ions that make up pure water. As a consequence, the taste of pure water might be described as very bland compared to a neutral background – because that neutral background would be the natural taste of our mouth which is dominated by saliva. Saliva itself is water with relatively high concentrations of sodium and potassium ions, which themselves taste salty. We are thus accustomed to a slightly salty taste which we perceive as normal, and by comparison pure H2O tastes less salty, and of nothing else – bland.