How would you describe the taste of water?

Let's say to an alien that's curious but scared to taste water cause they don't need it, i think one can argue that water has a taste, it's just an unexplainable taste cause there's nothing to really compare or too, it's not bitter or sour or salty or sweet, the best way to describe it is that it numbs your tongue without actually numbing it, a numbless numbness.
How would you describe the taste of water?
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