Everything Else . Since about the 1880's, when apartment and office buildings started regularly exceeding that height, rooftop water tanks have been needed to make sure faucets do not dribble weakly and to fill hallway standpipe reserves and sprinkler systems. In those buildings where the plumbing requires the help of gravity to create sufficient water pressure, a tank should be elevated at least 25 feet above a building's highest standpipe.
Wood is used rather than metal because it is both durable and cheaper to maintain than metal.
With good maintenance, tanks can last 40 years or more. New questions are answered on the site every Tuesday and Thursday.