Q. Kvod Harav.
Right before the beginning of the taanis, people often take a last drink of water. They are not thirsty then and it is only for preventing thirst later. Do they make a brocho on the water?

A. On question 1409, in regards to reciting a brocho when drinking water from a mineral spring that has therapeutic value and also has a good taste, we wrote;
“Poskim disagree if you drink water when you are not thirsty and you drink just for medicinal purposes, if you should recite a brocho. Some maintain that no brocho is recited, but you say a prayer for refuah. (Shaarei Halocho – Miluim 36, quoting Tzemach Tzedek). Others maintain that since after all the water is tasty, you should recite a blessing (Shoel Umeshiv 5: 23, Binyan Tziyon 10 and 3: 7, Sdei Chemed – Maareches Brochos 7). There is one opinion that even if the waters are not tasty you should express a blessing (Tehila Ledovid O.H. 204)
Horav Shlomo Miller’s Shlit’a opinion is that if someone feels a pleasant or desirable taste when drinking the mineral water (such as the bubbliness or effervescence of gas present or the flavor of the salts), he should recite a brocho even if he is not thirsty. The therapeutic value of the water is of no consequence.”
It would seem from the above that when people are not thirsty and only drink to avoid thirst later on, they should not recite a brocho, since they don’t derive any pleasure now.
However, Nitei Gavriel (Yom Hakipurim 23: 2) quotes that the Imrei Emes maintained you do recite a brocho. He explains that this may be similar to the ruling of the Biur Halocho (204: 7) that one recites a blessing when drinking water just to wash down the food one just ate. This is because he does derive pleasure and a good feeling, if not directly from the taste, but from the food now digesting properly in his stomach. Nitei Gavriel recommends to make a brocho omitting Hashem’s name.
Horav Shlomo Miller’s Shlit’a opinion is not to make a brocho, but the Rov recommends placing a bit of sugar or other product that will give a bit of pleasant taste to the water.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a