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.
Water supply and sanitation in Nigeria
Adequate sanitation is typically in the form of septic tanks, as there is no central sewerage system, except for Abuja and some areas of Lagos. A 2006 study estimated that only 1% of Lagos households were connected to sewers. Lagos has four wastewater treatment plants which have been rehabilitated around 2010. As of 2011, the state planned to build ten new "mega wastewater treatment plants" over the next five years with the help of private investors. These have not yet been completed.