Effluent sewer
Effluent sewers also currently serve fewer people than septic systems, which also use septic tanks, but simply dispose of the effluent by draining it into a leach field. About one quarter of United States homes dispose of their wastewater with septic tanks. However, effluent sewers are being looked at as a sewage treatment solution in areas where gravity sewer systems are not well-suited or when the high capital cost to build a gravity system is prohibitive. Areas that are less than ideal for gravity systems include areas that are large, but extremely flat and areas that require long-distance pumping, such as where homes are widely spread out or when several small villages or towns connect their sewage systems so that a centralized plant can be built.
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.