Prior to this, sewage was dumped into rivers and lakes and sometimes the streets. Because Chicago's landscape was so flat, the sewage didn't flow but remained stagnant. New technologies begin to be developed that allow for the "lifting" of city infrastructure, so the streets of Chicago are built up so that buildings are lifted off the bedrock, allowing for angled pipes to be laid below the city streets to carry the sewage out to rivers and Lake Michigan.
Additionally, the city reverses the flow of the Chicago River to send sewage downstream and away from the city's drinking water, eventually leading to the need for water treatment technologies to deal with the impact of the mounting sewage on those living downstream.