Charles Ellicott Commentary Numbers 20:2

"And there was no water for the congregation: and they assembled themselves together against Moses and against Aaron." — Numbers 20:2 (ASV)

And there was no water ... — Kadesh may have comprised a considerable portion of the wilderness of Zin, and there may have been a supply of water in some parts of the district and a scarcity in others; or the supply may have proved insufficient for the needs of such a large multitude; or the miraculous supply which was given at Rephidim may have continued, with more or less frequent intermissions, until the time being described, and may have been suddenly withdrawn at this time to try the faith of the Israelites.