If I stay in Beijing Gubei Water Town Hotel, should I pay also the entrance to the water town?

If you want to visit this water town, then you may need to purchase the admission fee. If not, you don’t need to. You can enter the scenic area only once with the one ticket and one ticket is available in 24 hours. The water town is just at the foot of the Simatai Great Wall, so you can walk there directly.