Albert Barnes Commentary Exodus 15:23

"And when they came to Marah, they could not drink of the waters of Marah, for they were bitter: therefore the name of it was called Marah." — Exodus 15:23 (ASV)

Marah - Now identified with the spring of Huwara. The fountain rises from a large mound, a whitish mineral deposit, deposited by the water, and is considered by the Arabs to be the worst in the whole district.