If you’re a zebra, a watering hole is the body of water you go to quench your thirst. If you’re a grown-up human, a watering hole is also a place that you go for a drink.
Your local watering hole is the pub or restaurant in your neighborhood where people meet for drinks, but mostly for conversation and companionship. A watering hole was originally "a source of water from which animals regularly drink," but some time in the 1960s it came to primarily mean "place (for humans) to socialize over drinks." A spa near the sea is also sometimes called a watering hole.