I have just added this to the map of places to fly your drone at Drone Scene:
Land owner permission requirements unknown.
Onsite Car Park. £3 at time of writing for all day.
As far as I'm aware Severn Trent Water have no policy specific to recreation/hobbyist flying, where as for commercial flying you must apply for permission.
Although check the discussion thread on Grey Arrows as this may have changed since time of writing.
The National Forest also have a stake in this location, but again I can see no specfic policy regarding drones at time of writing.
The TOAL marker is located on some picnic benches near the water tower. Early in the day or late evening will be your best bet to fly here without having too many members of the public in your shot for the water tower.
The rest of the reservoir is also nice and a pleasant circular walk around the site and into Calke Park can be done to make a day of it. If you decide to do that, take fluids and a picnic.
The originator declared that this location was not inside a Flight Restriction Zone at the time of being flown on 18/04/2022. It remains the responsibility of any pilot to check for any changes before flying at the same location.