I'm about 245lbs and 5'7. my doctor told me that i'm dehydrated. how much water and other fluids should i drink a day?

Maintain fluids: You weigh about 110 kilo. For that weight your maintainence fluids should be about 3400 cc/24 hr day or about 135 cc/hr or 4.5 oz/hr.

Depends: If you're not losing fluid by excess sweating,vomiting,diarrhea or abnormal frequency of urination such as occurs when taking diuretic medication or with uncontrolled diabetes, then drinking about 6 to 8 glasses of water daily should suffice. Soda,coffee,tea,etc also count but these shouldn't be drunk in large quantities. You should be putting out about a quart of urine daily if you're adequatel