For decades, storage tanks have been the primary resource to store municipal water and wastewater. Yet today's technology is making them tougher. "The use of post-tensioning in water storage and water treatment tanks has increased significantly over the past several years," says Dan Harger of VSL's Denver office. "Post-tensioned tanks have superior corrosion protection on the prestressing steel. And all cast-in-place concrete members are post-tensioned bi-axially to assure water tightness without joints in the floor or roof slabs." A case in point is the Foothills Water Treatment Plant in Denver where a circular, post-tensioned, potable water storage tank holds 25,000,000 gallons. Due to the circular shape, the load is evenly distributed around the tank. In many cases, tendon tanks are partially or fully buried to limit visibility and access. Since there are no coatings, joints, or liners required for water tightness, post-tensioned tanks are relatively maintenance-free and eliminate construction and maintenance costs associated with construction joints. "Since the prestressed steel strands are in tension and the concrete in tension," says Harger, "each material is in its ideal state."