A septic tank, the key component of a septic system, is a small scale sewage treatment system common in areas with no connection to main sewerage pipes provied by private corporations or local governments. (Other components, typically mandated and/or restricted by local governments, optionally include pumps, alarms, sand filters, and clarified liquid effluent disposal means such as a septic drain field, ponds, or peat moss beds.) Septic systems are a type of On-Site Sewage Facility (OSSF). In North America approximately 25% of the population relies on septic tanks; this can include suburbs and small towns as well as rural areas. In Europe they are generally limited to rural areas only.