Often they started out as settlement many years ago when there was sufficient surrounding land and an understanding of environmental concerns did not exist. The first sewer systems in such settlements were built at the turn of this century and in most cases emptied directly into an adjacent bay. Even now, often the untreated fluids and solids flow into the coastal waters. Over the years, all the available land has been taken for housing, commercial purposes, or infrastructure. Environmental concerns do exist now.
Coastal populations continue to grow.
So do sanitary concerns. The question is not what to do with the wastewater. Most of the built-up areas surrounding the Mediterranean Sea are situated in very specific conditions where the coastal patterns and historical urbanization limit the available space for land based sewage treating facilities. If a city council decides to take proper care of the sewage by building a waste water treatment plant, it must take in consideration the current state of its existing sewage system. Such systems are usually based on normal gravity float and the sewage discharges directly into the adjacent bay.