Who does? Not sure if you mean someone else or you have DID. Regardless though- might be worth them checking in with their doctor- excessive thirst and drinking can be an indicator of diabetes. May not be of course but might be worth checking. I don't know though. They recommend 2-3 litres anyway, so maybe it's not excessive. Do they consume a lot of salt in their diet? Or, live somewhere hot, or exercise a lot? Maybe their body is just narurally trying to compensate.