This page was last updated on 09 June, 2017.
1. The miracle
Exod 15:23 When they came to Marah, they were unable to drink the waters of Marah, for they were bitter; therefore one called its name Marah.
Exod 15:24 Then the people grumbled against Moses, saying: What shall we drink?
Exod 15:25 Moshe cried to ADONAI; and ADONAI showed him a certain piece of wood, which, when he threw it into the water, made the water taste good. There ADONAI made laws and rules of life for them, and there he tested them.
“Showed” has the sense of teaching something.
“Piece of wood” can among other things mean burned firewood.
“Bitter” is often used for salty. The “Great Bitter Lake” is salty. Click
That day God taught Moses the science of purifying water with charcoal. Even today charcoal is often used to purify water. While the Bible doesn’t mention any duration I think it must be assumed that the charcoal was in the well for hours before they drank the water.
A pound of charcoal thrown into a cask of water twelve hours before use, will purify it.