Foundation Plumbing Leak - A plumbing leak may occur either in a fresh water or sewage line. In expansive soils, a minor leak can cause the soil to swell and lift an area of a foundation. A major freshwater plumbing leak can lead to soil erosion and foundation slumping. A minor sewer leak will over time also cause soil erosion and foundation slumping. A foundation plumbing leak may be the cause of foundation failure, or may be caused by the failure of a foundation.