Like most nineteenth-century sewer systems, Washington's main lines discharged raw, untreated sewage directly into the Potomac and Anacostia Rivers, depending on the tides to flush sewage away from the city's waterfront. As the city grew in the late nineteenth century, the District's department of public works installed larger "interceptor" lines that gathered output from the ever-expanding grid of smaller local sewer lines. These interceptors gathered the city's output and transported it a distance from the original outfalls that were closer to areas with high population density. One outfall tunnel, built to gather sewage along the old city canal route, provides a route of evacuation several miles south of the city center. This spot is now home to D.C. Water's main treatment facility. Also note the placement of the interceptors, which tracks closely with the route of the old canal. This arrangement was meant to capture sewage before it could saturate the low-lying areas in the southwest quadrant, as well as to prevent recurring inundation in that flood-prone area.