Septic tank
While a properly maintained and located septic tank does not pose any more environmental problems than centralized municipal sewage treatment, certain problems can arise with septic tanks in unsuitable locations. Since septic systems require large drainfields, they are not suitable for densely built 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.