Nampa Prestressed Concrete Water Reservoir The Nampa Prestressed Concrete Water Reservoir is a 3 million gallon pre-stressed concrete water reservoir and pump house. This project is unique with 24 inch ductile iron piping, a 105 ft in diameter aluminum geodesic dome, and a 10 inch core wall with surrounding prestressing cables covered with shotcrete. Scope included 1,400 CY of concrete: tank footings, slab on grade and walls.