A slab leak is the most common plumbing problem and may stem from a variety of causes. A slab leak can also be called a “broken pipe” or “broken line”. The leak usually starts in the basement and may lead into the space under your house or it may simply seep water into the walls. Slab leaks account for over 50% of all residential plumbing problems.

What Causes a Slab Leak?

A broken underground pipe, usually caused by tree root intrusion or shifting soil. Tree roots can grow under concrete slabs and invade sewer pipes, leading to the need for a new sewer line at a substantial cost. If you want to avoid this problem, consider installing a French drain with root guards around trees that overhang your driveway or sidewalk where the roots are likely to attack the sewer pipe. The drain tiles will collect water from rain and melt snow and slowly release it into the ground instead of it being funneled toward the sewer line. This is a far cheaper solution than digging up a slab and replacing a broken sewer line. Sewage may also back up through shower drains due to tree root blockage of a lateral sewer pipe. Shifting soil, due to expansive clay soils or groundwater pumping, can also cause stress on sewer lines and cause them to eventually give way, leading to a slab leak. Tree roots may invade the joints of cast iron laterals but this is less common than with PVC laterals because metal has a tendency to corrode and dissolve tree root acids before they have a chance to do too much damage. Loosened connections in ABS or PVC plumbing running inside walls from foundation slabs being walked on due to poor construction practices is another fairly common cause of slab leaks.

A broken drain line inside the finished part of your house. A cracked drain line under a bathtub or shower usually indicates that it needs to be replaced.

Know more: https://en.wikipedia.org/wiki/Leak