In the wastewater treatment facility of Kalamata works of repair and strengthening of concrete on the reservoir of the stable sewage took place. The works specifically included the strengthening of the perimeter wall and of the walls controlling the sewage overflow by using reinforced shotcrete. Furthermore, the concrete structure controlling the overflow of the reservoirs and the perimeter walls were rehabilitated with repair mortars. Following the repair works, a crystalline technology product was applied on the concrete surface for reservoir waterproofing.