Tea acts as a diuretic because of its caffeine content and may therefore compromise hydration.
Experts now understand that for people who drink tea regularly, a tolerance to caffeine develops so any initial diuretic effect is diminished. It's common knowledge that adults should aim to drink two litres of fluids every day. Many people believe that tea dehydrates. Infact, drinking tea is actually better than drinking water because water is essentially replacing fluid and tea replaces fluids and contains antioxidants so it's got two things going for it.