One of our insureds has a commercial policy (ISO CP 00 10 04 02 with CP 10 30 04 02 attached) covering a large apartment complex. The complex is not connected to a public sewer; it has an on-site septic system.

Recently, the sewer line leading to the septic system backed up, flooding the lower units of the complex. The damage and clean up costs are extensive.

We think the loss is excluded, but the agent argues that a septic system is not a sewer, and the loss should be covered. His argument is that a sewer is public, but a septic system is private and as such is not a sewer.