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.
Septic tank
In many council districts (e.g. Sunshine Coast) septic systems have been banned and need to be replaced with much more expensive small scale sewage treatment systems that actively pump air into the tank producing an aerobic environment. Septic systems need to be replaced with any new building applications, regardless of how well the old system performed.