How much water should a German Shepherd drink in a day?

It depends on a lot of factors. How active is the dog and what is the climate like? When she is active in the summer it's not unusual for my 75 pound dog to drink up to a gallon a day. When she's inactive and it's also winter, she might drink as little as two quarts. The key is to make a fresh supply of clean water available to her nearly all the time. A healthy dog will self-regulate and drink the correct amount on her own. Withhold water only if she's drinking it too fast and vomiting it back up or right before an exercise period (which can also cause her to vomit).