
Sanitary sewers.
These carry wastewater from homes and businesses to main sewer lines and then to wastewater plants. This wastewater is then cleaned at these plants.

Storm sewers.
These move stormwater into a nearby body of water to prevent flooding around homes or businesses.

Combined sewers.
These carry both wastewater and stormwater to sewage treatment facilities. However, these types of sewer systems are not common anymore due to the difficulty of cleaning stormwater.