In general, animals should take in two and a half times more water than food. Dogs don't have to DRINK their daily fill of water. They also get water from the food they eat. Wet food has a lot more water than kibbles or dry food. Snacks like apples are also a great source of water.
When fresh, clean water is available a dog will generally drink all he needs to survive. The fresher the water, the more appealing it will be to your dog.
As a general rule, change the water in your dog's bowl at least 3 times a day.
Also, make sure your dog's bowl is clean. If you wouldn't drink from it, chances are he won't want to drink from it either. You need to wash your dog's water bowl every day and disinfect it regularly to control bacteria.