Storm water does not act as a distinctive factor for installation of sewer systems. The type of sewer installed depends upon terrain, where it is placed and uses. Sanitary sewers are most common type of system used to transport wastewater and industrial waste.

In separate systems, two sets of sewers are used to carry sanitary sewage and storm/ surface water separately. In combined system, a single sewer with a larger size is used to carry both sanitary sewage and surface water toger.

One of sewer wastewater treatment processes is a biological treatment known as activated-sludge process. Wastewater is agitated and aerated to remove solids and oxidation methods are introduced to activate decomposition.

Trench sewer construction is most common pipeline installation method. At grade level, sewers can be installed and protected by an embankment or a wall, or placed inside tunnel walls.

The velocity of 3 ft/sec is considered to be minimum to keep foreign particles moving in sewers. The Washington State Department of Health (DOH) recommends a maximum velocity of 8 ft/sec but permits greater velocities during fire flow conditions.

The high rate of flow of water can lead to increasing sound levels of flow which leads to noise. Hence minimum flow of water should be considered. 0.5-0.7 m/s is maximum velocity of tap water that produces less noise levels. 1.0-2.5 m/s of water flow leads to high noise levels.

To construct sewer systems certain rules and regulations have to be followed based on quality of pipes chosen, alignment and so on. Pipeline networks are designed by engineers based on city and installed by sewer contractors.

Open drains often carry storm water. In rainy seasons water level increases in drains. If it contains clogging or any operations to be done, it becomes difficult if depth is more.

If velocity is too less n solid or foreign particles which are very minute in size may settle down. Hence a minimum velocity is required to keep se particles moving along flow is likely to be 3 ft/sec.

If a city has less population, it consists of fewer residences and industries based on city needs. Hence quantity of sanitary sewage produced will also be less. It becomes uneconomical to lay separate sewers for both stormwater and sanitary sewage. Hence combined systems are preferred.