A cleaning logbook for the building's water tank

In many city buildings nobody remembers when the rooftop water tank was last cleaned. Dirt builds up and raises the risk of stomach illness and skin trouble, yet no one takes charge. Hang a logbook on the ground floor and pick one representative from each floor. Fix a day every few months to empty the tank, scrub it and check that the lid fits. Write the date and who did it in the book, and note when the next cleaning is due. You need one person per floor, a notebook and pen, a brush and buckets. Shared among everyone, the cost is small.