Water Back-Up (also known as Back-Up of Sewer and Sump Pump Overflow Coverage or by similar name in some states) provides coverage for losses from the back-up or overflow of sewers and/or drains. Overflow of sump pumps or other systems designed to remove subsurface water from the foundation are also covered, even if the loss is due to mechanical breakdown of the system.
I don't know how much this definition is relevant to your question but thought it may be able to help in some way. It may be a company by company decision but for us, if it is classified as a flood, waterbackup does not cover the damage.
I feel that insurance companies argue all the time about who covers a loss if a business has 2x companies. I think flood will only cover the definition of flood and water backup only covers the definition of water backup. I believe they are mutually exclusive and you need both, as flood will probably turn around and say "this is water backup, go to your homeowners policy" and the homeowners will go "this is flood, go to your flood policy."
