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.
Cistern
Some cisterns sit on the top of houses or on the ground higher than the house, and supply the running water needs for the house. They are often supplied not by rainwater harvesting, but by wells with electric pumps, or are filled manually or by truck delivery. Very common throughout Brazil, for example, they were traditionally made of concrete walls (much like the houses themselves), with a similar concrete top (about 5 cm/2 inches thick), with a piece that can be removed for water filling and then reinserted to keep out debris and insects. Modern cisterns are manufactured of plastic (in Brazil with a characteristic bright blue color, round, in capacities of about 10,000 (2641 gallons) and 50,000 liters)(13,208 gallons). These cisterns differ from water tanks in the sense that they are not entirely enclosed and sealed with one form, rather they have a lid made of the same material as the cistern, which is removable by the user.