A septic tank is a key component of the septic system, a small-scale sewage treatment system common in areas with no connection to main sewage pipes provided by local governments or private corporations. Other components, typically controlled by local governments, may include pumps, alarms, sand filters, and clarified liquid effluent disposal methods such as a septic drain field, ponds, natural stone fiber filter plants or peat moss beds. Septic systems are a type of onsite sewage facility (OSSF). In North America, approximately 25 percent of the population relies on septic tanks, including some suburbs and small towns as well as rural areas. Indianapolis is an example of a large city where many of the city’s neighborhoods are still on separate septic systems. In Europe, septic systems are generally limited to rural areas. Since septic systems require large drainfields, they are not suitable for densely built cities. The term “septic” refers to the anaerobic bacterial environment that develops in the tank which decomposes or mineralizes the waste discharged into the tank. Septic tanks can be coupled with other onsite wastewater treatment units such as biofilters or aerobic systems involving artificially forced aeration. Periodic preventive maintenance is required to remove solids that remain and gradually fill the tank, reducing its efficiency. Maintenance requires regular pumping to remove these. According to the US Environmental Protection Agency, in the United States it is the home owners’ responsibility to maintain their septic systems. Those who disregard this requirement will eventually be faced with costly repairs when solids escape the tank and clog the clarified liquid effluent disposal system. A properly maintained system will likely not need replacement during the homeowner’s lifetime.