Is it permissible to water a pig if it is on the verge of death from thirst, and would that carry the same reward as watering a dog, and how do we reconcile this with the Hadith about Jesus (peace be upon him) killing the pig at the end of time?

He who finds an animal on the verge of death from thirst and gives it water will be rewarded for that, because the Prophet, peace and blessings be upon him, said: "In every wet liver there is a reward."

This includes animals commanded to be killed, such as pigs. They should be given water then killed as an act of kindness towards them, because kindness is obligatory in everything, even in killing.

The descent of Jesus, peace be upon him, to kill pigs is to demonstrate the corruption of Christian beliefs and to affirm the law of Islam, and it does not contradict showing kindness to them.