Cleansing the Water
What made the water at Marah bitter? A huge underground water supply is underneath the Sinai desert, which drains near the eastern and western coasts. This water is rich in sulfates, which are bitter, and when ingested is a strong cathartic. (Glauber’s salt, sodium sulfate, is given medicinally as a cathartic, but it is too bitter for some people.) Not only is it bitter, but is also dehydrating — life-threatening in desert summer heat.
Breccia is calcified wood, in which the wood fibers have been replaced by calcium (similar to petrified wood, in which the wood fibers have been replaced by silica). Calcium sulfate is nearly insoluble (solubility only about 0.3% by weight). If breccia is the “tree” Jehovah showed Moses, then powdering it and adding it to the bitter water, then calcium sulfate (gypsum, or plaster of Paris, building materials) will precipitate and leave the water suitable for drinking. And this technique could be used not only at Marah, but throughout the journey down the west coast of the Sinai peninsula and then up the east coast.
— Br. Jim Parkinson
At Elim there were 12 wells and 70 palms.