Direct one-time leaks occur infrequently and are due to specific conditions. Leaks may be the result of wind-driven rain into cracks or an abnormal early spring when melting snow cannot penetrate the frozen soil and instead finds its way down the side of the foundation where the soil is permeable due to heat loss.

Seepage may occur on a regular basis, but at a slower rate than direct leakage. This is noticeable in the fall or spring when heavy rainfall and melting snow cause the soil around the foundation to become saturated with water. The weeping tiles may not be able to carry the excess water away, subsequently, it seeps into the basement. Note that weeping tiles (or footing drains) were not commonly installed for homes built before 1950. Many are no longer effective due to deterioration, clogging or poor design, for houses that are 20 years or older.

Condensation is a significant source of basement moisture. When the basement air is humid, the moisture in the air condenses on cool surfaces such as cold water pipes, foundation walls or floor slab.