Do we know who were the three Giborim?
Radak (39): Avishai (verse 18) was one of them; the other two are not named.
Malbim (24): They were Avishai, Benayahu and Asah'el (listed after this).
Why did he not want to drink it?
Radak (15-16): After they brought it, he retracted that he endangered these three Giborim due to his craving for the water. He thought that drinking it would be like drinking their blood, for they brought it via [risking] their lives.
Malbim citing Mahari: It is proper that the purpose correspond to the efforts. It was awesome Gevurah for three men to break through the enemy camp, draw water and on the return fight while holding the water 1 ! David did not want that such great efforts be for a small matter, rather, for a great matter, to pour it on a Mizbe'ach to Hashem.
Refer to 23:16:3:1,2.
Malbim: (What is the source that they fought on the way back? Perhaps Pelishtim were not concerned if they return with the water! - PF)
What is the meaning of "he poured out the water as a libation to Hashem"?
Rashi (from Bava Kama 61a): (The water was asking a question to the Sanhedrin.) He had a tradition that one who endangers himself for Divrei Torah, we do not say the Halachah in his name. Rather, it was merely cited as a tradition. 1
Bava Kama 61a: He was told that a commoner may not [use others' money to save himself, or feed his animal's from Yisrael's food on condition to pay, but a king may. He declined to rely on the special Heter for a king.
Radak: He poured out the water l'Shem Hashem. There was no Mizbe'ach there 2 !
Malbim citing Mahari: He poured it on a Mizbe'ach (i.e. he built a Bamah) to Hashem. 3
Even though the Halachah would be said in the name of the Chacham of the Sanhedrin who said it, normally we mention also the one who said it in his name; this brings redemption to the world (Avos 6:6)! However, why was it not said in the name of the Chacham of the Sanhedrin, who did not transgress?! (PF)
Radak (verse 15) himself explained that David built a Bamah, which was permitted then! That was according to a Drashah; here he explains according to simple Pshat. (PF)
Kli Yakar: If David asked for water to drink, why would they guard it in Taharah? Mahari explained that David did not ask them. They realized that perhaps he will not drink it, so they guarded it in Taharah. (Even though Chaverim eat and drink b'Taharah whenever possible, this is not so feasible in war, and surely they needed to kill Pelishtim to break through! Surely they took the water in a Kli Cheres with a Tzamid Pasil, to guard it from Tum'as Mes. (PF)
