For some Availability PPP Projects, the Services as defined in the services specification in the PSDR may distinguish between providing availability for use as a service component and providing related outputs as a separate service component. For example, on a water desalination plant project, the availability of Project Assets for water treatment may be separated from the production of treated water. These 'fixed and variable' arrangements suit circumstances where the State values the opportunity to pay Project Co separately for availability and for outputs, particularly where there is uncertainty about the variability of the State's requirements over time for specific outputs.