Start with where the water emerges
These are clues, not a diagnosis. Rain can contribute to both groundwater intrusion and sewer backups, so “it happens during storms” does not settle the question. From a dry, safe location, photograph the first visible entry point rather than only the puddle after it spreads. Do not enter water to investigate.
Groundwater pressure: investigate beneath the slab
Water accumulating around and beneath a foundation can exert pressure against it. Foundation and sub-slab drainage systems manage that water; a sub-slab system can lower the groundwater level immediately beneath the building and direct water toward a sump.
Record which crack, joint or penetration becomes wet first and how its timing relates to rainfall. When outdoor conditions are safe, observe from ground level whether runoff collects beside the foundation or downspouts discharge nearby. These observations give the drainage specialist something specific to investigate.
Ask the specialist to assess existing drainage, any sump system and the proposed discharge route before recommending new equipment. Request a written explanation of how the repair addresses water beneath the floor. Federal building-science guidance warns that crack sealing and floor coatings alone cannot resolve serious intrusion caused by conditions such as poor grading or a high water table.
Drain backup: have a plumber trace the route
Water flowing upward from a floor drain, basement toilet or other low plumbing fixture calls for a plumbing investigation. Tell the plumber whether other fixtures were slow or gurgling and what appliances were operating when the water appeared. Do not deliberately flush toilets or run laundry to reproduce the problem.
Ask the plumber to distinguish a blockage or defect in private drainage piping from water pushing back from the public sewer during wet weather. What inspection would establish the difference, and would a camera inspection help? Do not open cleanouts or attempt sewage cleanup yourself.
A backwater valve allows wastewater out while closing against reverse flow through the pipe. It addresses that backup route, not groundwater entering through concrete. Ask which fixtures a proposed valve would protect, how roof drainage affects the arrangement, and what maintenance it requires.
Standing water changes the first call
Never operate electrical tools, pumps, appliances or switches while standing in water. If reaching the electrical panel requires entering water, call an electrician rather than attempting it. Electrical equipment exposed to flooding needs professional evaluation before being returned to service.
Treat possible sewage contamination as a reason to use qualified cleanup professionals, not merely a wet vacuum. EPA advises assuming mold growth when a flooded home and its contents have not dried within 24–48 hours. Arrange safe cleanup promptly while the plumber or drainage specialist investigates the source; removing water does not establish why it entered.
White powder is a moisture clue, not the answer
A white mineral residue on concrete may be efflorescence. Water moves through porous material and evaporates, leaving salts and other deposits behind. That explains a moisture pathway, but does not identify the source of an active floor-water event.
Photograph the residue and note whether it follows the same cracks or joints that become wet. Ask the inspecting professional to connect the deposit to observed moisture movement rather than treating the powder alone as proof that a particular drainage repair is needed.
For Philadelphia homes: reporting, permits and public help
If the home is in Philadelphia, call the Philadelphia Water Department hotline at (215) 685-4901 while water is still present to report an apparent sewer backup, and contact a private plumber. The department encourages reporting during the event so the flooding can be documented.
Before permanent plumbing changes, have a licensed master plumber identify the required L&I permits and inspections. Philadelphia exempts clearing stoppages from a Plumbing Permit, but installing or altering plumbing is a different scope. Private water or sewer service work follows the Site Work / Utility Permit process.
Separately, Philadelphia’s Basement Backup Protection Program offers qualifying properties free backwater-valve installation and downspout modifications when needed. Ask the program to confirm eligibility. This public assistance targets wet-weather sewer backups; it is not a general remedy for water seeping through a basement slab.
Related HomeFix guides: what to document when water appears in a basement; interior drainage versus exterior waterproofing; whether a sump pump needs battery backup; and Philadelphia sewer-lateral permit questions.