In a research conducted on coffee and hydration, researchers compared people who drank coffee and people who drank only water. In the research, no major difference was found in the level of water in the body of both the categories. The research results did not find clear results on dehydration, which weakened the notion that drinking coffee in normal amounts dehydrates the body.

The caffeine present in coffee is considered a mild diuretic, meaning it can increase the amount of urination. For this reason, it has been believed that coffee removes water from the body, although experts say that this belief is based on old research.