Septic tank
In the United States, the 2007 American Housing Survey indicated that about 20 percent of all households rely on septic tanks, and that the overwhelming majority of systems are located in rural (50%) and suburban (47%) areas. Indianapolis is one example of a large city where many of the city's neighborhoods still rely on separate septic systems. In Europe, septic systems are generally limited to rural areas.
Tankhouse
There are far more tankhouses in California than in any other state, and they most probably originated in California. A tankhouse was built in Mendocino, California, in 1857 and many tankhouses in a variety of designs are still standing in that village. Tankhouses can be found in most of the state's 58 counties, wherever there was water not more than 50 feet or so below the surface. Probably after transcontinental and branch railroads were completed, tankhouses were built in other western states, the midwest, and even in the east.