Bees clustered near water

On Q Street, in Sacramento, a front yard has a small waterfall, very zen-like. Around the edges of the water bucket cluster bees (wasps?):

Bees collect nectar, pollen, propolis (plant resin) and water for their colonies. On very hot days, you'll see scores of bees at a water fountain, bird bath, or pond.
... 

Flottum points out: "Water is as necessary to your bees as it is to your pets and to you. Whatever watering technique you choose for your bees, the goal is to provide a continuous supply of fresh water. This means while you are on vacation for a couple of weeks, when you get busy and  forget to check, and especially when it's really, really hot--bees always need water."

"Water is used to dissolve crystallized honey, to dilute honey when producing larval food, for evaporation cooling during warm weather, and for a cool drink on a hot day," Flottum writes in his book. 

Via: http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=11349