Typically 55%RH plus or minus 5%RH is a comfortable and practical humidity level for an indoor pool area.
It can be varied depending on the season, to minimise operating costs. When the weather is colder, condensation forms more easily on walls and surfaces. So setting 50%RH would be ideal. During the summer, this can be allowed to rise to 60%RH, reducing energy consumption and operating costs, whilst still avoiding condensation.