Availability and reliability evaluation of chilled water and electricity generation of a cogeneration plant depend on individual components availability and reliability in particular the electricity and chilled water generation system. This paper deals with modeling of chilled water availability and reliability of a cogeneration power plant using probabilistic and reliability block diagram approach. The under study cogeneration plant consists of four main components namely; gas turbines (GT), electric chillers (EC), thermal energy storage tank (TES) and steam absorption chillers (SAC). These components exist with three possible states: full working, reduced capacity working and failed. To incorporate all three states, multi-state theory is adopted. A transition and reliability block diagram represent the operational behavior and logical order of the system. Availability and reliability of chilled water system are compared with actual and traditional availability and reliability using statistical evaluation. Results of the study could be useful to develop a proper and effective maintenance strategy for a system. © 2011 IEEE.