Consuming coffee and caffeinated beverages does not cause dehydration.

noli's read

The idea that caffeine causes dehydration is a persistent myth stemming from old and limited studies. Current research, notably a meta-analysis published in PLOS ONE, confirms that for habitual consumers, caffeine has a negligible diuretic effect that does not compromise overall hydration. The volume of liquid consumed via coffee largely offsets the slight increase in urinary excretion, which allows for the maintenance of adequate fluid balance. These conclusions are supported by randomized controlled trials (RCTs) showing that moderate caffeine consumption does not lead to a significant difference in hydration markers compared to water alone. It is, however, important to note that in non-habitual consumers, an acute diuretic effect may be observed, but it fades quickly with tolerance. The statement is therefore scientifically sound and clarifies a persistent misconception.

the sources

1. 1Valtin H 2002