Identification

• Identify the exact location of the leak to repair it. Release dark food coloring from a syringe slowly into the concrete pool water. The leak sucks the coloring toward itself and draws it out. Mark the spot on the base or wall of the pool with a grease marker.
  
  

Considerations

• Sometimes leaks occur in inground pool equipment such as the pump, filter or fittings. This is indicated by food coloring flowing with the pool water and not drawn to any leak. Inspect the pool equipment for leak indicators such as excess moisture. Tighten the particular fitting with a hose clamp to prevent it from leaking, or replace the piece of equipment in extreme cases.
  
  

Leak Repair

• Drain the water from the pool and examine the location of the leak you marked with a grease marker. Use a grinder to extend the crack 1/4 inch longer at each corner and 1/2 inch deep. Apply pool patching plaster inside the crack with a utility knife. Also spread it 1/2 inch around the crack. Leave the plaster to dry overnight.