these systems did not improve much over the years. there were almost no improvements from the time of the roman aqueducts and sewers until the 19th century. eventually the development of separate, underground water and sewage systems got rid of open sewage ditches and cesspools. most large cities today send solid wastes through pipes to sewage treatment plants. treatment separates water from waste and makes the water more pure before it goes into streams or other bodies of water. most places stopped using lead for drinking water after world war ii because of the dangers of lead poisoning. at this time, copper piping was started because it was safer than using lead pipes.