The amount of water consumed by dairy cattle depends on their size, their productive state (growing, lactating, etc.), the environmental temperature, and other factors such as water quality and dietary factors. At about 80°F dairy cattle will consume (gallons/day) the following amounts of water:
dry cow (non-lactating) = 16 gallons/day
lactating cow producing 70 lb of milk = 30 gallons/day
600-lb heifer = 10 gallons/day