Why does my dog drink a lot of water?

If it is excessive and out of the ordinary, talk to a vet. I have had two dogs with sudden excessive water drinking and both had serious medical problems that caused it. One had kidney stones. The other had cushings, a serious hormonal imbalance.

Drinking excessive amounts of water is often a sign of an underlying medical problem. Three of the more serious medical problems that cause a dog to drink excessive amounts of water include kidney failure, diabetes, and Cushing’s disease

If your dog's water intake changes significantly, there may be a medical condition. However, some dogs drink more than others or at certain times (when panting, at play, in hot environment, resource guarding, or if diarrhea).

Possibly played so much that they're dehydrated. As Ye their food too fast and it made them thirsty. If they're crate trained and don't have access to water bowl they might be thirsty when the get let out at the end of the day.