Design of the Sewer System. The sewage system plays a vital role in the economic development of a country. Sewers are mandatory for sewage drainage. In order to have an effective sewage system the sewers must be properly designed and more care should be taken in the pursuit of investment levels otherwise whole design may be wrong. Design of the Sewer System. Sewers are designed for sewage drainage from homes, industries, streets, runoff, etc. to protect the environment and people from serious diseases, such as more than 50 diseases spread sewage. So for a good life, sewers should be properly designed and sewage must be properly treated before discharge into the river.