Waste water treatment is designed to process waste water whilst protecting the environment and maintaining public health. Outfalls to the marine environment fall into three categories:
- outfalls from waste water treatment (WWT) plants which process waste water from the mains sewerage system (this layer);
- industrial sites which take waste from manufacturing plants (see separate layer - Industrial (SPRI) marine discharges); and
- some private domestic sources (not on NMPi).
These categories of outfall also discharge to the riverine freshwater environment which eventually reach the sea.