This kind of drinking problems is more frequent during the summer months, when the poor dogs get so thirsty sometimes that they will drink whenever they see water.
Hydration is even more important to dogs since their body is made up to 80% of water, and that is why every time they take a sip of water it needs to be as clean as possible.
Stagnant water only has risks for your pup beginning from different kind of bacterias, parasites, viruses up to even hair or dust that has gathered on his surface. Yuck yuck yuck!
The most important tip is to never let the dog tell you he is thirsty, because if so you will never approve his choice to satisfy his thirst. Provide them constantly clean water in their bowl.
A dog needs up to one ounce of water everyday. If you are not careful enough and let their bowl of water go gross they will end up looking for water elsewhere, so make sure to provide fresh water at all times.
Wash their bowls everyday. This is the only way to make sure it is bacteria free.
Even when you are outside the house walking your dog, come prepared. Take a bottle of water with you always.