Daas yochid, if you “just want to hydrate yourself for health reasons”, that is ?????. If you are dehydrated then you need water, therefore you are thirsty. It is exactly the same as eating flavorless food when you are malnourished; how could you possibly imagine that this would not be called ???????, or that you would be exempt from a bracha? The principle here, as always, is ???? ????? ????? ??? ??? ????, so a bracha is necessary if and only if there is ????. Eating flavorless food, or drinking plain water, when one is full and hydrated, produces no ????, therefore one says no bracha. Doing so when one is malnourished or dehydrated, i.e. hungry or thirsty, produces ????, therefore one does say a bracha. Anything else is ?????????.
