Percolation is a process in which water passes through a porous material, such as soil or rock, and is filtered and purified. This process is often used to clean and purify water for drinking. Leaching is a similar process, but it involves the movement of dissolved substances from one material to another. In this case, the term 'leaches' refers to the movement of water through a porous material, such as soil or rock, and the removal of dissolved substances from the material.