Includes the drainage network (pipes, sewers, canals, ditches, retention ponds, etc.), stormwater and wastewater pumping stations, wastewater treatment plants and other auxiliary works for the purpose of collecting, conveying, draining stormwater and wastewater, preventing inundation, and treating wastewater. Drainage systems are classified into the following types:

– Combined drainage system is a system in which wastewater and stormwater are collected in the same system;

– Separate drainage system is a system with separate stormwater and wastewater drainage networks;

– Semi-separate drainage system is a combined drainage system with interceptor sewers to separate wastewater and convey it to treatment plants.