I would say "מים זה טעים" or "מים הם טעימים".

I came here with the same question! :)

In Hebrew water (מים) is considered plural

Words that end in -ayim used to be dual (in contrast to singular or plural, for two things) and take plural adjectives. Hebrew doesn't have proper dual words anymore, but historically-dual words still agree with plural words.

Not in Israel