great question.
The halacha is that we say a bracha when (a) there is nutritional benefit and/or (b) the taste buds get pleasure.
Water has 0 calories (therefore, no nutritional benefit) and it has no taste (so the taste buds get no pleasure from it). if, however, you are thirsty or you desire to drink water, then there’s pleasure so a bracha is necessary. if you’re drinking so that you will not become thirsty in the future (e.g., before a taanis), it’s a machkoles as to whether a bracha is necessary.
if you want to make a bracha, or you’re ever in doubt as to whether or not you’re thirsty, say it on something else and have in mind to exempt the water.
hope this helps.