Or HaChaim on Genesis 24:19/אור החיים על בראשית כ״ד:י״ט

1 ותכל להשקותו, When she completed giving him to drink, etc. Seeing that the Torah does not describe Eliezer as having finished drinking, it is clear the Torah wants us to know that she kept bringing him water until he stopped drinking.

2It is also possible that Rebeccah judged when Eliezer should stop drinking, seeing that weary travellers who have gone without water for a long time are not the best judges of when they may be drinking more than is good for their health.

3We may view the matter also in light of what the Talmud teaches in Berachot 40, based on Deuteronomy 11,15 that one must feed one's animals before eating oneself. This ruling applies only when there is no danger to the life of the person involved. If his life is in danger, concern for his own health takes precedence over the wellbeing of his animals. When Rebeccah heard Eliezer ask for some water she concluded that she faced a man whose need for water was immediate. This is why she said to him: "drink!" As soon as she had given him sufficient water to ensure he was not in danger of dehydrating she suggested giving water to his camels, the ones which normally should have been looked after first. This is why the Torah phrases Rebeccah's action in such a way that we understand that as soon as was practicable she turned her attention to the camels, giving them to drink. She added that she would continue until the camels had finished drinking, meaning that in the case of the camels she was not going to rely on her personal judgment of when the animals had had enough to drink. She kept drawing water for the camels until they stopped drinking.