any source of water works fine. just make sure there is a big enough surface for the number of bees you have and that they will not drown in it. i use the bottom of an old stock tank. poultry waterers work. even a dripping faucet with some gravel at the bottom.
train them to the water source so that they (hopefully) stay clear of your pool. a little sugar in the water, or some lemongrass, oil will help. you'll still get the occasional bee where you don't want them, but once they are used to a consistent water source, they will use it most of the time.