A homeowner in a mid-sized Ontario city returned from a 10-day vacation to discover standing water throughout the basement of her 35-year-old detached home. The damage was extensive: finished drywall saturated to a height of approximately 45 centimetres, laminate flooring buckled and lifted, a home office with electronics and stored documents ruined, and a persistent sewage odour permeating the space. The total claimed loss would eventually be quantified at approximately $87,000, including structural remediation, content replacement, and mould abatement.

The homeowner held a standard homeowners policy with a major Canadian insurer, purchased 4 years earlier when she acquired the property. At the time of purchase, her insurance broker had discussed optional coverages with her, and she had added sewer backup coverage with a $25,000 sublimit. She had declined overland flood coverage, noting that her property sat on relatively high ground in a neighbourhood that had never experienced surface water flooding in her recollection. The policy contained standard exclusions for water damage, including exclusions for surface water, groundwater, and water that enters through foundations or basement walls, alongside the typical insuring agreement language requiring covered losses to be "sudden and accidental."

Investigation by the insurer's adjuster revealed a complex causation picture. A significant rainfall event had occurred 3 days into the homeowner's absence, dropping approximately 78 millimetres of rain over a 6-hour period. Municipal storm and sanitary sewer systems in the neighbourhood had been overwhelmed, and several nearby properties had reported basement flooding through floor drains. However, the adjuster also noted evidence of longer-term moisture issues: staining along the base of foundation walls predating the loss event, a sump pump that had failed at an indeterminate time, and a basement window well with deteriorated caulking that showed signs of chronic water infiltration. The weeping tile system, original to the home's 1989 construction, had never been inspected or maintained.

The homeowner had installed a battery backup for her sump pump 2 years earlier but had not tested it in the 8 months prior to the loss. She had received a notice from her municipality 18 months earlier encouraging homeowners to install backwater valves, but she had not acted on that recommendation. The insurer's engineering consultant concluded that water had entered the basement through multiple pathways: reverse flow through the floor drain during the storm event, seepage through the foundation walls that had occurred gradually over an extended period, and possible surface water entry through the compromised window well.

The claim file now presents questions about which portions of the loss fall within the sewer backup endorsement, which portions are excluded as gradual damage or surface water intrusion, whether the homeowner's mitigation efforts or failures affect her coverage entitlements, and how the "sudden and accidental" requirement applies to a loss with both acute and chronic contributing causes.