This incentive applies to one- and two-family homes, whose sprinkler systems are governed by NFPA 13D. The standards allows multipurpose systems, which combine the sprinkler system with a home's plumbing system. Because all of the water in the system is potable, there is no need for a check valve or backflow preventer and thus a lower cost. One trade can install both. The reduction of the number of subcontractors on the job makes coordinating simpler for the builder.