To provide a service water and sewerage maintenance and management system and a computer software whereby any maintenance and management firm having a knowhow allowing judging totally the function of any plant can conduct a maintenance and management of the service water and sewerage.

The service water and sewerage maintenance and management system includes a device 1 to be installed in each maintenance and management firm to conduct a plant maintenance and management of a service water and sewerage facility 2 composed of a plurality of apparatuses 21 and equipped with a communication device 15 connected with a network circuit 4 for transmitting and receiving information, wherein the device 1 is furnished with an operational information collecting means 11 to collect a plurality of pieces of plant operating information via the network circuit 4, a plant diagnosing means 12 to make diagnosis on the basis of the collected pieces of plant operating information, and an operation execution planning means 14 to execute and plan the operation and maintenance of the plant.