When your rented property includes a water feature you must meet your landlord obligations for how you keep both it and the surrounding areas safe for the use of your tenants and any visitors to the property.
When it’s your responsibility to open the pool please make sure you diarise to get this done in good time to ensure your tenant can enjoy the pool during warm weather.
When you manage the property yourself be sure to use appropriately qualified contractors to do any required works at or around the water feature.
The best scenario is to put a maintenance and servicing contract in place and laid out in the tenancy agreement rather than leaving it up to the tenant to maintain.
Ensure any water checks and subsequent chemical additions are done in good time to be confident the water is safe for when the pool is opened.