The first mention of bitter water in the Bible is Exodus 15:23. As the Israelites traveled in the wilderness, they came to a spring of water. But when they tried to drink it, they found that the water was bitter. The word translated “bitter” is marah in Hebrew, and that became the name of the place. The water may have had a salty, metallic taste and was undrinkable in the way that ocean water is undrinkable. There still exist springs in that region with bitter-tasting water. God miraculously transformed the water of Marah from bitter to sweet (verse 25).
A puzzling use of the term bitter water is found in Numbers 5:11–31. As part of the Israelite Law, bitter water was used to determine whether or not a wife had been unfaithful to her husband. This is a different type of bitter water than we saw in Exodus. The bitter water of Marah appears to have had a natural cause, such as sediment or pollution from an unknown source. But the bitter water in Numbers 5 is pure water taken from the tabernacle laver and mixed with dust from the floor (verse 17). The priest was to write down the accusations against the woman, as well as the accompanying curses on a scroll, swish the scroll in the water, and make the accused woman drink the bitter water. If she was innocent, nothing would happen, and she was free to go.
If, however, the woman had committed adultery, after she drank the bitter water, “her womb shall swell, and her thigh shall fall away, and the woman shall become a curse among her people” (Numbers 5:27, ESV). There was clearly nothing in the water that would cause it to taste bitter or cause such extreme physical conditions. The power was in the curse that the Lord’s priest pronounced upon the guilty. It was the Lord’s judgment on an unfaithful wife that caused the adverse reaction.
God often used natural items to bring about supernatural results. In the trying of an adulterous wife, the Lord used water mixed with dust to reveal the truth. The bitter water was used by God to bring a bitter judgment on sin.
Revelation 8:10–11 speaks of another kind of bitter water. When God pours out His righteous wrath on the earth in the in the last days, one phase of this punishment is called the trumpet judgments. The third trumpet judgment is described this way: “Then the third angel sounded his trumpet, and a great star burning like a torch fell from heaven and landed on a third of the rivers and on the springs of water. The name of the star is Wormwood. A third of the waters became wormwood, and many people died from the water, because it had been made bitter.” Wormwood is a woody shrub used in making medicine and is known for its bitter taste. “Bitter as wormwood” was a common metaphor because everyone knew how unpleasant it tasted. Wormwood is also used to describe bitterness of soul and experience. In the end-times judgment, the “bitter” water must also be poisonous because people die from drinking it.
So, in the Bible, bitter water can refer to water that is actually contaminated and tastes bitter. It also refers to water that God uses in a supernatural way to accomplish His purposes. And bitter water can be used metaphorically to describe a life of sorrow and turmoil resulting from disobedience to God (Jeremiah 9:15).