But despite what you've heard, coffee and caffeinated tea are not dehydrating, experts say. ... It's true that caffeine is a mild diuretic, which means that it causes your kidneys to flush extra sodium and water from the body through urine.

Is drinking tea good for hydration?

Researchers report that when consumed in moderate amounts, caffeinated drinks — including tea — are as hydrating as water.

Can I drink tea instead of water for hydration?

Coffee and tea also count in your tally. Many used to believe that they were dehydrating, but that myth has been debunked. The diuretic effect does not offset hydration.