Water requirements for beef cattle depend on weight, stage of production such as lactation, and temperature. As you increase weight, the amount of water needed also increases. The same holds true for temperature; as temperatures increase, so does water intake. Also, if the animal is lactating, water requirements increase.
Here are some guidelines:
Assuming 70 degree temperature, 1,100 pound cow, non-lactating = 9 gallons per day.
Assuming 70 degree temperature, 1,100 pound cow, lactating = 20 gallons per day.
Reference: NRC, Nutrient Requirement of Beef Cattle, seventh Revised Edition, Update 2000