my dr put it this way: tho phentermine (the drug in duromine) isnt an amphetamine, they are related, and like amphetamines, the phentermine will 'speed' ur body up. While its mainly a drug that helps people who overeat to control their bad habits by working as an appetite suppressant, it also does speed up ur metabolism and does burn stored fat. So as it 'speeds', ur body needs the extra water to prevent dehydration, as well as potential headaches, spacey feeling, sweats, and dry mouth.
If i make sure i drink 3 to 4 litres a day and i hardly get any side effects.
By the way, drinking alot of water with meals actually slows down digestion; ur stomach digests liquids before solids so try not to drink alot with ur meals.