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I drink a lot of coffee and have done so for years. These days I drink less coffee in terms of volume than ever before but the coffee I do drink is a bit more potent.
For a while my wife has been telling me that I need to drink other "non-coffee" drinks to stay hydrated but without going out with a purpose to do so I've always done pretty good.
I can't help but recognize the fact that drinking large volumes of coffee almost always means I'm going to have to go pee in the new couple hours but I'm not 100% sure this is due to the diuretic effect of the caffeine or because of the quantity of fluids I'm taking in.
In fact lately as I've been drinking a lot of espresso and potent french press coffee I've probably been going pee less frequently than before. Even though I'm drinking more caffeine per ounce of fluid I'm not experiencing the same diuretic effect so this led me to this small blurb posted by the Mayo Clinic's Katherine Zeratsky.
"Drinking caffeine-containing beverages as part of a normal lifestyle doesn't cause fluid loss in excess of the volume ingested. While caffeinated drinks may have a mild diuretic effect — meaning that they may cause the need to urinate — they don't appear to increase the risk of dehydration." Source
This kind of answers my question - If coffee is a diuretic then why do I not ever seem to get dehydrated while drinking it?
Looks like the water content in coffee offsets the fluid loss caused by an increased need to urinate after drinking coffee. In short it's a wash.