New York City's combined sewer system, built largely in the late 19th century, routinely backs up during heavy rain, pushing Category 3 contaminated water into basement apartments across all five boroughs. With roughly 46 inches of annual rainfall and increasingly intense nor'easters, the risk is citywide and year-round.
Pre-war masonry construction is especially prone to envelope failures during sustained rain events. Superstorm Sandy in 2012 caused an estimated $19 billion in damage across the city, flooding subway tunnels and entire neighborhoods — a reminder of how fast losses cascade in dense, multi-unit buildings.
IICRC S500 protocols govern certified restoration work in New York City. If you rent, New York's Housing Maintenance Code obligates your landlord to maintain a watertight building — document all damage before cleanup and call a certified crew immediately to start the drying clock.