The owners said their planned £80m development at the site in Bewdley, Worcestershire, would create between 300 and 500 jobs.
Wyre Forest District Council granted planning permission for the water park, including seven slides. The park said it hoped this would open by 2017.
The hotel was given outline planning permission.
Some people living in Bewdley have raised concerns about traffic congestion and the impact on the environment.
Managing director Ivan Knezovich said: "If we see the safari park as a destination, the whole idea of creating a destination is for people to say 'well let's go to Bewdley, let's go to the safari park and we'll have a two or three days stay'.
"(That) means it'll encourage people to travel out into the Wyre Forest, to the River Severn."
Stephen Williams, who chairs the planning committee on the council, said the positives outweighed the negatives.
He said: "This is a very, very major development and it will bring a great deal of employment."
Proposals for an indoor water park and a hotel at West Midland Safari Park have been approved by councillors.