Many jurisdictions now require a reduced-pressure-zone backflow preventer instead of a check valve. This adds a substantial cost to the installer, who must pass the cost to the builder and ultimately the home buyer. This has created more interest in multipurpose systems, which combine the sprinkler system with the potable water system. Because there is no stagnant water in the system, a check valve or backflow preventer is not necessary. At present, multipurpose systems are only allowed in one- and two-family homes.