Septic tank
In the United States, the 2007 American Housing Survey indicated that about 20 percent of all households rely on septic tanks, and that the overwhelming majority of systems are located in rural (50%) and suburban (47%) areas. Indianapolis is one example of a large city where many of the city's neighborhoods still rely on separate septic systems. In Europe, septic systems are generally limited to rural areas.
Atlanta metropolitan area
Sewerage is also handled by the water utilities, but the various water and sewer networks may not conform to the same boundaries, resulting in interbasin water transfers. This is for practical reasons, because the area is hilly and divided by several watersheds, because the area has developed irregularly and erratically, and because water treatment plants are usually not near sewage treatment plants. Septic tanks are still used in the older homes of some exurbs.