marah

Marah
bitterness, a fountain at the sixth station of the Israelites
(Ex. 15:23, 24; Num. 33:8) whose waters were so bitter that they
could not drink them. On this account they murmured against
Moses, who, under divine direction, cast into the fountain "a
certain tree" which took away its bitterness, so that the people
drank of it. This was probably the 'Ain Hawarah, where there are
still several springs of water that are very "bitter," distant
some 47 miles from 'Ayun Mousa.