The large size of the K&H Pet Products Coolin' Water Bowl For Dogs and Cats ($27) is perfect for big dogs, because it can hold up to 96 ounces of liquid that'll keep cold for up to 15 hours (there's also a 32-ounce option available). The brand said dog owners need to activate the K&H Cooling Crystals by filling the bowl with water before the first use, then emptying it and freezing it overnight. "For extended cooling power, freeze about an inch of water in the bowl each night," the company recommended.