King James Bible Dictionary

Bitterness, a fountain at the sixth station of the Israelites (Exodus 15:23, 24; Numbers 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.

The first station of the Israelites, where Moses made the bitter waters sweet.
Exodus 15:22-25; Numbers 33:8-9

(bitterness), a place which lay in the wilderness of Shur or Etham, three days journey distant, (Exodus 15:23; Numbers 33:8) from the place at which the Isr'lites crossed the Red Sea, and where was a spring of bitter water, sweetened subsequently by the casting in of a tree which "the Lord showed" to Moses. Howarah , distant 16 1/2 hours (47 miles) from Ayoun Mousa , the Isr'lites' first encampment, has been by many identified with it, apparently because it is the bitterest water in the neighborhood.