There's a water fill and dump station both at the entrance to Lone Rock Beach. In the event that either is closed, you may also do so just down the road at the Wahweep Marina Campground.

Theres a water fill and dump station in the park

The Pilot between Beehive and Lone Rock on Hwy 89 has free dump and potable water. They also have a air station/compressor that I think is also free, to fill the inflatable toys close to the lake.

Pilot gas station about 1 mile down the road also has dump and water.

Pretty sure there is a dump station at the park mgr lot just after the entrance. Not sure if water is there too. Worst case you may have to drive to Page.

The water isn’t potable