Bees need quite a lot of water to survive. In hot weather they may spend as much time collecting water as they do nectar. Honeybees use it to cool the hive and to dilute the honey they feed to larvae. However - and this might seem like stating the obvious - bees cannot swim or stand on waters surface so they need to be able to drink from some for of platform or get their water from damp material. Floating plants work as a platform or muddy gradual pond edges where they can suck form the banks. Beekeepers should consider how close their hives are to the nearest source of water because longer journeys will put stress on the hive.
At rosybee we have put in a wildlife pond with graduated sides. The grass has now grown back at the edges and into the water itself. You can see in this picture how the bees find the water in the wet pond edges.
If you are a gardener you might want to think of providing a watering hole for pollinating insects - some capillary matting with one end in a reservoir of water will work. or a shallow tray filled with pebbles that will soak the water up.