A method and drilling fluid system for providing filtration control during drilling operations using a drilling fluid system comprising water soluble polymer comprising acrylamide monomer, the method comprising: providing a drilling fluid system having effective rheological properties, the drilling fluid system comprising aqueous base consisting essentially of freshwater, a quantity of from about 21 to 58 kg/m3 (7.5 to about 20 pounds per barrel) plugging agent, and an amount of bridging agent comprising water soluble polymer comprising acrylamide monomer which exhibits a 5% by weight Brookfield viscosity in freshwater of from about 50 cP to about 100 cP, and; contacting a subterranean formation with the drilling fluid system and maintaining effective filtration control at concentrations of about 10,000 ppm or less monovalent salt, as demonstrated in the laboratory by producing a HPHT filtrate of 25 cm3/min or less after 30 minutes at about 149° C. (300° F.) after static aging of said drilling fluid system for a period of 16 hours or more at temperatures of about 260° C. (500° F.).