A slab leak is usually caused by pipe corrosion, abrasion where lines rub against concrete or rebar as they expand, high water pressure, poor installation or kinks, and foundation and soil movement that stresses the pipes under the slab. In North Texas, expansive clay soil makes that ground movement a common trigger.
Corrosion is the most common cause in older homes. Copper and galvanized steel lines react with the soil around them and the water inside them until the metal thins and weeps. Water chemistry drives this: the U.S. EPA sets a recommended pH of 6.5 to 8.5 and notes that water outside that range corrodes pipes and leaches copper and other metals. The signs and repair side sit in this wider overview of slab leaks.
Abrasion adds to it. A supply line expands and vibrates as hot and cold water run through it, and where it rubs against concrete, rebar, or gravel a wear point opens over time. High water pressure speeds that up, and a pipe dented or kinked during installation starts with a weak spot. The two leak types behave differently: a supply-line (pressure-side) leak pushes water out constantly and shows up sooner, while a drain-line leak only seeps when something drains and can stay hidden much longer.
Ground movement is the cause homeowners here feel most. North Texas expansive clay swells when wet and shrinks in drought, and that repeated shift pulls on the pipes beneath a slab, the same soil movement behind clay-soil pipe damage across DFW. It often combines with corrosion or an old weak spot rather than acting alone. Because the causes overlap, the only reliable way to confirm which pipe is leaking and why is professional water leak detection, not a guess from the surface.