Seepage is when liquid is being absorbed into to some kind of material (It is moving from one place to another, where it should not be present). A leak is the the fact of of liquid being lost. e.g. "There is a leak in the pipe and water is seeping into the wall/ ground/ woodwork. We need to resolve this problem of seepage."

Leak is usually used when there is a loss of material from a system that was created for moving that material. The material can be a liquid, gas or solid. Seepage usually happens when a liquid slowly moves through an environment independent of an intended system for movement.

Seepage means the the slow escape of a liquid through porous material or small holes, while leakage is the accidental escape of liquid through a larger hole or crack.

Seepage is a water that seeped or oozed through a porous soil while leak is the entrance or escape of a fluid through a crack, fissure, or other aperture

Seepage is the process by which a liquid leaks through a porous substance; the process of seeping.