WHY COLOR CODE HYDRANTS? THE 2 MAIN REASONS FIRE HYDRANTS HAVE THEIR BONNETS PAINTED A DIFFERENT COLOR THAN THE LOWER BARREL ARE SIMPLE... 1.  TO SHOW WHAT THE HYDRANT'S OUTPUT CAPACITY IS (in Gallons per Minute). ACCORDING TO AWWA - COLORS ARE DETERMINED AS FOLLOWS: GREEN = > 1000GPM (FLOW GPM AT 20 PSIG) ORANGE = 500-1000GPM (FLOW GPM AT 20 PSIG) RED = < 500GPM (FLOW GPM AT 20 PSIG)     2.  TO SHOW WHAT THE HYDRANT'S MAIN SIZE IS. FOR EXAMPLE ONLY: ORANGE = 24" MAIN GREEN = 12" MAIN WHITE = 8" MAIN YELLOW = 6" MAIN     *** PUMPER TRUCKS FIND COLOR CODES USEFUL IN DETERMINING THE SUCTION PSI. THEY WILL TEND TO BACK OFF ON A 6" MAIN OR LESS TO PREVENT COLLAPSING (CAVE IN) THE MAIN PIPE UNDERGROUND WHICH WOULD STOP THE SUPPLY OF WATER!