A cistern is just a tank to hold water. I would check to make sure it’s secure. If it’s in the ground could anyone fall in? could kids get into it? If it’s near a parking lot is it in a area where it would collapse if someone drove over it? What is it used for? Drinking water could be contaminated from parking lot run off. If it’s used to water the grass does it have a pump? Check any elec. for GFI. Where does it get its water from? Gutters, storm drains? do they need covers to keep large debris out?
If it is used in any way that someone might drink from it I would recommend a plumber evaluate it.
That’s all I can think of for now.
I’m going to Wendy’s for a cheeseburger, anyone want anything?