Mine wont work - someone watered my farm 3 which only has flowers and trees so its not really a problem but I think the neighbours watering is sill blocking the use of the red sprinkler. Im not getting a mouse over to say how many hours until next use unlike the other farms and I have found that when there is no mouse over hours showing I can usually use it.
Ha Ha just found the secret! It WILL work if there are crops but not if only flowers - obvious really.