The sewerage system in Poland, built in the early 20th century, needed rehabilitation to restore its water-tightness and flow capacity. Trenchless technology was used to add a new leakproof layer to the sewers without digging up the streets. Two methods were compared: one using GRP panels and the other using CIPP lining. After rehabilitation, the flow velocities and rates in the sewers were improved. This approach is cost-effective and environmentally friendly compared to traditional excavation methods.