There are different types of septic treatment systems to treat household waste water, with or without an on-site effluent disposal system. The type of system required for a particular home will depend on a number of factors, including the size and slope of the property; its soil type and natural drainage patterns, to determine the most appropriate disposal system; the amount and type of waste water to be treated; and any governmental conditions, recommendations or requirements for the installation. There may be two tanks to separate the gray and black water on-site, or there may only be one tank that treats all the site's waste water. The treated water from septic tank systems may be disposed via common effluent drain systems, or via an on-site effluent disposal system.
Standard septic tank installations for the home offer a sustainable option for on-site waste water treatment that is natural, inexpensive to run, and low maintenance. The waste water is treated by bacteria in the septic tank where solids and waste are broken down before the 'effluent', or treated waste water is then disposed of. The quality of the effluent partly depends on how long the water remains in the tank before disposal.
In some systems, the effluent from each property is sent to a common collection point, where it is treated further before disposal (common effluent drain system). Alternatively, on-site effluent disposal systems are available with septic tank installations for the home. These consist of absorption trenches, where water is allowed to absorb into the ground; however, septic tank waste water can also be diverted via an underground irrigation system to directly water the lawn and garden. Other types of on-site effluent disposal systems include mound systems, sand filter systems, and soakage wells; these types are used mainly where the site consists of rocky or heavy clay soil, or where it is in a high rainfall climate or the water table is high.
Septic tank systems need to be the correct size to fit the number of household occupants. If they are too small, or if they are designed or constructed poorly, they may fail or prove inadequate for the task. Maintenance should also be carried out as required, in order for septic tank systems to remain the most cost effective way to treat and dispose of household waste water. This is particularly important in remote areas, where many homes are reliant upon a septic treatment system because it is the primary or only waste water treatment system available.