text: By a wide margin, wet pipe sprinkler systems are installed more often than all other types of fire sprinkler systems. They also are the most reliable, because they are simple, with the only operating components being the automatic sprinklers and (commonly, but not always) the automatic alarm check valve. An automatic water supply provides water under pressure to the system piping.
  Wet systems have optionally been charged with an antifreeze chemical, for use where pipes cannot reliably be kept above .
  While such systems were once common in cold areas, after several fires which were not controlled because of sprinkler systems filled with too high a percentage of antifreeze, the regulatory authority in the United States effectively banned new antifreeze installations.  A sunset date of 2022 applies to older antifreeze systems in the US. This regulatory action has greatly increased costs and reduced options for cold weather tolerant sprinkler systems.