The Israelites were tired, drained...
The Israelites were tired, drained, and edgy from their traveling. They were living on bare subsistence in the wilderness and needed rest. This wasn't a little caravan of people, but a mass of humanity attempting to stay in some orderly fashion just to make a few miles a day. Coming to Rephidim, which means "resting place," they were irritable, irrational, and frustrated. They had been wilted by the scorching sun and were thirsty beyond normalcy. All they wanted was a cool drink of water... but oh no, not with their "luck." The brook, which at times watered the valley floor, was dry.