Basement wall crack leaking water — Den Haag, Zuid-Holland

Water seeping through cracks in basement walls is one of the most common — and most ignored — home problems. Hairline cracks in poured concrete walls are normal as concrete cures and the house settles, but once water finds a path, hydrostatic pressure from saturated soil drives it through relentlessly. A damp streak or mineral deposit (white efflorescence) along a crack means water is actively moving through. Small non-structural cracks can be sealed from the interior with epoxy or polyurethane injection ($300–$800 per crack), which fills the crack through the full wall thickness. If multiple cracks are leaking, the exterior drainage system may be failing — clogged or collapsed footer drains, negative grading pushing water toward the foundation, or missing downspout extensions. A waterproofing contractor can install an interior French drain system with sump pump ($3,000–$8,000) or excavate and waterproof from the outside ($5,000–$15,000 per wall). Wide cracks (over ¼ inch), stair-step cracks in block walls, or cracks that are wider at the top than bottom indicate structural movement — these require a structural engineer's assessment before any waterproofing work.