The consumption of a cup of Coffee (and many Teas) will remove an equal amount of water from your body plus an additional 20%.
So it is a very good idea to always drink water before either beverage.
Tea is pH value 6,
Coffee is pH value 5.
It increase Acidity in the Body. Acidity causes lot of major diseases like Cancer, Ulcer, etc..
It’s not that tea or coffee will cause cancer, but it helps keep the body in an acidic environment if it is not neutralized.
Drinking glass of Water before the Tea and Coffee will minimize the damage