Drink all the water you can!!
Amphetamines tend to be pretty good diuretics - as all of us on them can attest to (I pee and pee when the meds are working). If you find yourself with dark urine and the urge to pee a lot, then you are probably getting dehydrated.
I find myself with dry mouth and frequent urination most days. Also, the meds tend to perk you up and you get more done so you naturally sweat out more of your water.
I drink a good 8 liters or more a day of water. I work in a factory and sweat a lot and drink water every half hour to an hour - and bathroom breaks whenever possible. My urine stays normal colored if I'm drinking enough. It's a good barometer and I can tell you my meds work great!