The Jews leave Egypt and they are THOISTY! They arrive in a place called Marah but they can't drink the water there כי מרים הם - Because the [water] was bitter. [Maybe at the seder we should have bitter water in addition to the bitter herbs. I have a good friend named Herb and he is not bitter at all].
But wait. The sentence doesn't EXPLICITY say that the WATER was bitter. It says that "they" were bitter. Maybe, suggested the great Polish Sage known as the Kotzker, it wasn't the water that was bitter but the JEWS. When the Jews were bitter they couldn't drink the water because it tasted bitter. When a person is bitter even sweet things seem bitter.
If you have a positive attitude about life you will see everything positively. Others who have a negative attitude see everything negatively. We determine in advance what our experiences will be [to a certain extent]. Let us all decide to put on rose colored glasses and view the world positively. It feels GREATTTTT:).
Sabbatical Salutations SWEETEST friends.