It is well-known that before drinking water, one recites the Beracha of "She’ha’kol Niheya Bi’dbaro." What many people do not realize, however, is that in some situations, one should not recite a Beracha before drinking water. The Mishna in Masechet Berachot establishes that "Ha’shote Mayim Li’sma’o" – "somebody who drinks water to quench his thirst" – must first recite the Beracha of "She’ha’kol." The Gemara (44) infers from this comment that if a person drinks water to dislodge a piece of food stuck in his throat, he does not recite a Beracha. The Mishna speaks specifically of drinking water to quench one’s thirst to indicate that in a case where someone drinks water for a different purpose, such as to release something caught in his throat, no Beracha is recited.
A number of Halachic authorities, including the Gaon of Vilna (Rabbi Eliyahu of Vilna, 1720-1797) and the Ben Ish Hai (Rav Yosef Haim of Baghdad, 1833-1909), expand the Gemara’s ruling to include any situation where one drinks for a reason other than thirst. A very common example is somebody who drinks water when swallowing a pill. A person in this case would not recite a Beracha over the water, unless he is thirsty at that moment, in which case he derives enjoyment from the water and must therefore recite a Beracha. Likewise, if a person is dehydrated or at risk of dehydration, and he is advised to drink water despite the fact that he does not feel thirsty, he does not recite a Beracha before drinking. Since he drinks water to fill his body with water, rather than to quench thirst, no Beracha is recited. A similar case arises before fast days, when people often drink water to store in their bodies for the fast. A person who drinks for this purpose does not recite a Beracha, unless he happens to feel thirsty at that moment.
The work "Mishne Halachot" applies this Halacha to seltzer, as well. Seltzer, like water, does not have any flavor, and therefore, according to this view, one does not recite a Beracha over seltzer unless he drinks it to quench his thirst or he derives enjoyment from the taste. But if he drinks seltzer for one of the purposes mentioned above, such as to swallow a pill or to hydrate his body, then he would not recite a Beracha.
Summary: One does not recite a Beracha before drinking water unless he drinks for the specific purpose of quenching his thirst. If he drinks water for some other purpose – such as for swallowing a pill, in preparation for a fast, or to avoid dehydration – then he does not recite a Beracha, unless he happened to be thirsty at that moment, in which case the water also serves to quench thirst.
