Exodus 15:23

Overview - Exodus 15
1	The song of Moses, Miriam, and Israel on their deliverance.
22	The people want water in the wilderness.
23	The waters at Marah are bitter, they murmur, Moses prays, and sweetens the waters by God's direction.
27	They encamp at Elim, where are twelve wells, and seventy palm trees.

Exodus 15:23  (King James Version)
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.