The bees use water to keep hydrated, but they also use water to regulate the temperature in the hive and around the brood section of the nest. The hotter the weather, the more they need. Specific bees get the task of being water carriers and spend the entire day making trips back and forth to the water supply the scout bees have located and shared with them. They will continue to use the same source as long as it remains an available option, much like they do with a nectar source.
Dr. Tom Seeley, the Horace White Professor in Biology in the Department of Neurobiology and Behavior at Cornell University, and his team have done some amazing studies with honey bees and is always fun to learn from their work. He has several lectures on YouTube about honey bee behavior, one in particular describes how they discovered that once a specific bee comes to gather water and lands on a select location, like a rock for example, that bee will return to the same rock each time she come to collect more water. They use safe paint, like the Posca fabric pens use for marking queens, to mark individuals so they can easily identify the bees in these type studies. This enables efficient subject identification and accurate verification.
Below are some examples and helpful tips for helping provide a clean water source for the apiary.