Sewer may refer to:
- Part of sewerage, the infrastructure that conveys sewage
- Effluent sewer, a collection system that transports only the liquid portion of wastewater through small-diameter pipes laid at contour
- Sanitary sewer, a system of pipes used to transport human waste
- Storm drain, a collection and transportation system for storm water
- Combined sewer, a system performing both the functions of a sanitary sewer and a storm sewer
- Sewer, one who does sewing