Our intrepid island MacGyver, always looking for redemption and forgiveness, lands in grotto water once again. We've seen Sayid lament the path that his life took before, and seeking a better life to make amends for his transgressions is not new to him. In what he believes are his final breaths he now asks Hurley, "When I die, what do you think will happen to me?" Little does he know, but Hurley finds out soon enough.
It looked to me like Jacob has some important plans for Sayid, as he intently ponders his near lifeless body on the ground. He looks deep in thought about something. If the water did 'turn' and lose it's power because Jacob died, then Jacob possibly knows something about the waters that the temple Others don't yet. But before they learn the fate of Jacob and the waters, they submerge Sayid in the pool face down on Jacob's relayed commands to save him.
I wonder, is it necessary for the dying person to inhale the water before they die to be healed, and to die in the water? That's a lot like Christian baptism, "dying" to sin and being washed by the waters of the Holy Spirit, becoming a "new man" in Christ as the Bible puts it. I follow the sprinkling method myself but theology aside, I can see the case for total immersion here. Sayid's body later revives, after an odd reaction by Miles over his seemingly lifeless body. Did Miles know that there was something different going on there in Sayid? Or that it wasn't Sayid? In typical Lost fashion, when questioned Miles replies with the usual, "Nothing." Grr-arg! It also looked like the shot hole in his shirt was gone, but that could have just been the camera angle.
We don't know why the unclear water worked anyway but perhaps it was because while not present physically anymore, Jacob is still around spiritually and his powers are weaker but still somewhat viable. And since now that the water was apparently less potent, did it just not heal Dogen because he only dipped his hand in briefly? Sayid asked the correct question, "What happened?"