Gemara

(Mishnah): One who drinks water due to thirst blesses [beforehand] sheha'Kol Nihyeh bi'Dvaro;

R. Tarfon says, he blesses Borei Nefashos Rabos v'Chesronan [Al Kol Mah she'Barasa - some delete these words].

Question (Rava bar Rav Chanin): Whom does the Halachah follow?

Answer (Abaye): Go see whom people follow!

Berachos 44b (R. Yitzchak): One blesses Borei Nefashos after eating even Yerek, but not after water.

(Rav Papa): One blesses afterwards even for water.

(Rav Ashi): When I remember, I follow both of them.

Question (against Rav Papa - Mishnah): There is something that requires a blessing beforehand but does not require a blessing afterwards.

Answer #2: This refers to fragrances.

Question: Why does the Mishnah say "one who drinks water due to thirst"?

Answer (Rav Idi bar Avin): This excludes one who drank because he was choking on meat.

Rishonim

Rambam (Hilchos Berachos 8:1): One blesses sheha'Kol before water, and afterwards Borei Nefashos. If one drinks it not to quench his thirst, it does not require a Berachah before or after.

Rosh (Berachos 6:43): One who drank water because he was choking on meat does not bless, for he did not benefit. One benefits from drinking other drinks and from their taste. One must bless on them even if he drank due to choking. This is like we say (36b, regarding olive oil) "one might have thought that since it is for Refu'ah, he need not bless. [Rav Yehudah] teaches that since he benefits, he must bless." Rav Amram Gaon brings from Rav Paltoy that he does not bless before drinking, due to Ones (choking), but afterwards he blesses Borei Nefashos. I disagree. He does not bless because he does not benefit. This applies equally afterwards! Rather, he need not bless at all. Also, according to Rav Paltoy, why did we say that "due to thirst" excludes drinking due to choking? This is obvious. This is Ones! Rather, this exempts even from a Berachah Acharonah.

Rashi (14b DH R. Tarfon): I heard that R. Tarfon comes to obligate even a Berachah Acharonah. This is wrong. We ask according to Rav Papa, "what requires a blessing beforehand but not afterwards?" We did not challenge R. Tarfon! Rather, R. Tarfon discusses a Berachah Rishonah.

Note: I do not understand Rashi's question. The Gemara preferred to challenge Rav Papa (an Amora), because R. Tarfon (a Tana) could argue with the Mishnah!

Tosfos (45a DH Rebbi): Do not say that the first Tana holds that we bless only before water, and R. Tarfon holds that we bless even afterwards. If so, what was the question against Rav Papa? R. Tarfon holds like him!

Tosfos (44b): Our custom is like Rav Ashi. We bless Borei Nefashos after water.

Tosfos (45a DH d'Chanaktei): He is exempt from blessing only regarding water. One benefits from water only when he drinks it for thirst. Hana'ah of ceasing to choke is not considered Hana'ah. The body benefits from other liquids, so one blesses on them in any case. We say (36b) that even one who drinks [olive oil] for Refu'ah blesses.

Poskim

Shulchan Aruch (OC 204:7): One who drinks water due to thirst blesses sheha'Kol and afterwards Borei Nefashos.

Sha'arei Teshuvah (12): Batei Kehunah says "some leave a Revi'is [of coffee] to cool off [so they can drink it quickly and bless afterwards]. People do not enjoy it this way! Batlah Daitam (we ignore their opinion). The Halachah is based on normal people. (One does not bless afterwards.) This is like we say about Kutach [a dip. Even if one consumes a k'Zayis of Chametz bi'Chdei Achilas Pras, he is exempt, for] it is abnormal to eat it so quickly. One must eat normally [to say a Berachah Acharonah]." I disagree. One says a Berachah Acharonah even for water drunk for thirst! Do not explain that since it is not Derech Hana'ah, Batlah Daito, and he does not bless sheha'Kol beforehand. Surely this is not so! One must bless on any Hana'ah, unless it damages.

Mishnah Berurah (40): This is not only if he was truly thirsty. Stam, as long as the palate enjoys the water, he is somewhat thirsty, and he must bless. If he was not thirsty at all, the palate would not enjoy it.

Bi'ur Halachah (DH ha'Shoseh): The Ro'oh explains 'this excludes water', i.e. people drink it only for thirst. I.e. Stam, people drink it only for thirst, for otherwise one does not benefit from it. If one knows that he did not drink for thirst, without benefit, rather, for another reason, like we will explain, he agrees that one does not bless, just like one who was choking. The Rambam connotes like this. He did not mention choking, for this is merely a typical case. If not, why does he drink? The same [exemption] applies to all similar cases. Aderes (Shnos) Eliyahu (the Gra on Berachos 6:8) explicitly says so, and also Tosefes Shabbos (Likutim). If so, if one drinks water just to join towards [a Zimun for] Birkas ha'Mazon [according to the Magen Avraham, who says that he joins], or he drinks a Revi'is to cover a Safek about a Berachah Acharonah, if he knows that he has no Hana'ah from the water, he does not bless, and he may not join.

Bi'ur Halachah (ibid.): The Poskim connote that if one drinks water to soak the food in his stomach, this is called for thirst. Even though we do not bless on water during the meal, this affects one who drinks after the meal in order to soak.

Eshel Avraham (Butshats): If I am unsure whether I drink for thirst, I bless sheha'Kol on something else. It seems that all agree that one blesses afterwards even if he drank without thirst. This is like one who ate Isur or a food not so proper to eat. Since he ate it, this shows that he considered it a food [so he blesses afterwards].

Note: The Rosh said that since one did not benefit from water [that he drank due to choking], also afterwards he need not bless! The Bi'ur Halachah says that drinking a Revi'is does not help for a Safek Berachah Acharonah if he has no Hana'ah from the water! It seems that Eshel Avraham retracted in his latter edition.

V'Zos ha'Berachah (5762 edition, p.114): Tea without sugar is like water. One who drinks it blesses only if he enjoys the taste (ha'Gaon R. Y.S. Elyashiv Ztz"l, Shevet ha'Kehasi, Eshel Avraham Butshats). Ha'Gaon R. S. Z. Auerbach, Ztz"l says that one always blesses for a drink with artificial taste, even if it has no calories (Pischei Halachah 1:96).

Note: I saw in the name of the Chazon Ish that a Berachah Acharonah on water is not such a Chiyuv.

Shulchan Aruch (ibid.): If he was choking on meat, and drank water to make the meat go down, he does not bless before or after.

Beis Yosef (DH u'Mah): Rav Amram obligates a Berachah Acharonah for one who was choking. The Tur, Tosfos, R. Yonah, Mordechai and Rosh disagree.

Magen Avraham (18): If one drank something else to make the meat go down, he blesses, like in Sa'if 8.

Mishnah Berurah (42): If one drinks other liquids or eats a piece of bread, which the palate enjoys, even if he ate or drank only because he was choking, he blesses on it before and after. When one drinks water in the morning for Refu'ah, he does not bless. If it is also for thirst, he blesses.

Kaf ha'Chayim (38): If one blessed Borei Nefashos beforehand, he was Yotzei the Berachah Rishonah, and he does not bless afterwards (Birkei Yosef, unlike Ma'amar Mordechai). He should think sheha'Kol in his heart before drinking, or as long as he did not finish drinking, and think Borei Nefashos afterwards.

Kaf ha'Chayim (46): If one was choking and drank a Revi'is, it is good to fulfill Rav Amram's opinion through eating something on which he must bless Borei Nefashos, or at least to think the Berachah in his heart.

Orchos Chayim (Levinger): If one drinks much water to loosen his bowels, he need not bless. However, perhaps this is unlike due to choking. The Tur brings from R. Yonah that one does not bless for water drunk for Refu'ah.

Question: If one needed to bless Borei Nefashos, and forgot, and urinated, and then remembered, which does he bless first? He was obligated first to bless Borei Nefashos. Or, since he did not bless it in time, he should bless Asher Yatzar in time, and then Borei Nefashos?

Answer (Maharshal 97): He blesses Asher Yatzar first. Whatever is Tadir (more frequent) has precedence. Asher Yatzar is considered Tadir, for one can go several days without saying Borei Nefashos, e.g. he eats and drinks only within meals. Also, there is no Shi'ur [how much one must eliminate] for Asher Yatzar, like the Rosh says, but there is a Shi'ur for a Berachah Acharonah. It is proper to say first a Berachah without a Shi'ur.