The hot temperatures lead to more water loss. Firstly your dog will pant more and this leads to water loss through drool. Furthermore, they may forget to drink while playing in the warm weather which then creates a cycle of drooling and not replenishing the water. Furthermore, if you take your dogs on long walks or leave them out to play in the backyard it is important to check they have water available. Beyond that, try to call in your dog often for a drink break as they may get too excited and forget to do so.