How much water does a calf need in winter?

Usually when it snows the wind blows and drifts the snow.  The wind is needed in winter to drift the snow to allow our cows to graze. We use no hay and the cattle here have to graze all winter. When the wind bares up ground, this provides the grazing needed to keep the animals full. Last March I went to check on our weaned heifer calves. The pasture they were in is very hilly and hard to get around in the pickup. After several attempts to locate them, I decided they were probably tucked in behind a hill and it was better off leaving them alone to wait out the storm. On Tuesday, I knew they had not had water since Sunday and I located them about 1/2 mile south of the windmill. I called them within about 200 yards of the well and gave them some protien cake. They had been in this pasture most of the winter so I was not worried about them going to water. On Wednesday, I went back and was surprised to see there were no tracks in the snow going to the windmill. After they ate their cake, they drifted east and never went near the tank. This got me wondering how often the actually drink from tanks in the winter. I have heard cattle may only drink once every couple of days in the winter and have reports from Canada where cattle will eat snow most of the winter to supply their water needs. Were they eating enough snow to supply their needs for water? They only know and I guess they will drink from the tank when they are good and ready.