Thats what i'll look into is a bird bath of some sort...You say you added Rock salt to the water??? How much rock salt per gallon of water do you add??
I did not actually measure it. Sorry. I would say that 1/4tsp is pretty close to what I placed directly to the bath. Salt does not evaporate so do not add it again.
I rinsed the pea gravel well before putting it in the bird bath to remove all powdered sediment. I fill the bath up just enough to wet the gravel and keep it moist for a few days. The bath is in the shade of a few saplings as are the hives. The hives are painted white on the tops, with screened bottom boards. I will post a pic if you want.
They have not had any problems with heat build up and comb collapse thus far. I hope they don't but July and August will be the true test! It gets very hot here. They are set in a field to get ample sun and just at the edge of the saplings. I mainly tend to them between 10:00 and 11:00 A.M. so I will be less apt to break the comb from the bars.