First, rule out a sewer backup
In much of Philadelphia, rain and snowmelt drain into the same combined sewer as household wastewater. When that sewer is overwhelmed, water can push up through floor drains, basement toilets and sinks. That's a different problem from foundation seepage, and the fix is different too.
- Water coming up through a floor drain or fixture, especially with a sewage smell, points to a backup. The flood guide says to call the Philadelphia Water Department before you pump it out, so PWD can inspect and sample the water.
- PWD's Basement Backup Protection Program provides free plumbing upgrades, such as backwater valves, to homeowners whose basement fixtures back up in wet weather.
- Water seeping through the wall, along the wall-floor joint or through slab cracks, with no drain involved, points to groundwater or surface runoff. That's a grading, gutter or drainage job.
Keep out of any standing water that may contain sewage, and never touch switches or plugged-in equipment while you're standing in water (CDC returning-home safety guidance).
Where the water shows up first tells you the route
Mark the first wet spot, not the final puddle. A puddle can cover several possible entry points.
- Under a basement window, with snow or water in the well: the well isn't draining, or runoff is pouring into it. Check it from above; don't climb in.
- One corner or one stretch of wall: often roof water from a single downspout or a low spot where a snowbank is melting against the house.
- The wall-floor joint or floor cracks on several walls: rising groundwater under the slab. Building America notes that paint and sealers alone can't fix serious water entry from poor grading, missing gutters or a high water table (basement floor guidance).
- Sump pit filling faster than usual: expected in a thaw. It's only a problem if the pump can't keep up or the discharge is blocked. See how to test a sump pump before snowmelt and where the discharge line should go in winter.
What to check outside, from safe footing
During the melt, walk the outside and look for puddles against the wall, snowbanks shoveled up against the foundation, and downspouts that dump right at the house. Building America's benchmark is ground sloping at least 5 percent away from the foundation for the first 10 feet, which is about 6 inches of drop (pre-retrofit basement assessment). The city guide also asks residents to keep storm inlets clear of snow, leaves and trash, since a blocked inlet can back water up toward homes.
The same guide says to make sure area drains are open and working. Many rowhomes have a paved back yard that empties into one small area drain. If snow or ice covers it, meltwater can pool against the back wall, so clearing it when it's safe to reach is a cheap first test.
Leave icy gutters, roofs and frozen drain lines to a contractor.
Keep a short thaw log for whoever you hire
For each event, write down when the snow fell, when melting started, whether it rained too, when water first appeared inside and where. Note whether a plain rainstorm causes the same leak. A few photos of the outside pooling and the first wet spot give the contractor something to test against.
Which pro to call, and what to ask
- Backup through drains: PWD first, then a licensed plumber. A backwater valve installed outside the city program needs a licensed plumber who pulls the L&I permit, per the flood guide.
- Overflowing gutters or downspouts at the wall: a gutter or roofing contractor.
- Seepage at the joint, cracks or window wells: a basement waterproofing or drainage contractor. Our guide to interior drainage versus exterior waterproofing explains the two approaches, and Philadelphia's permit rules for waterproofing and sump pumps cover what needs a permit.
- Bowing, displaced or badly cracked walls: a structural engineer before any waterproofing.
Ask any contractor what evidence shows where the water gets in, whether the plan keeps water away from the foundation or only manages it inside, where pumped water will discharge, and how you'll know it worked during the next thaw.
Once it's safe, dry wet materials quickly. The EPA says drying damp areas and items within 24 to 48 hours keeps mold from growing in most cases (EPA mold and moisture guide).