3 ms·Even sewage, which is less complex, only makes sense in dense areas. Many homes have septic tanks.by koheripbal 6y agoEven sewage, which is less complex, only makes sense in dense areas. Many homes have septic tanks.jjeaff 6y agoWhich is why we have sewage systems in dense areas and septic systems in rural areas.barumi 6y ago> Even sewage, which is less complex, only makes sense in dense areas. That's ok, as over half of all mankind lives in dense urban centers.