Real-time control (RTC) can be either heuristic or model based. Model-based control is theoretically more optimal, but due to the ease of implementation, heuristic control is more commonly applied. Generating sufficient evidence that RTC is a suitable option for CSO mitigation remains problematic, although new performance methods might make this possible. Regulations United Kingdom There is in the UK a legal difference between a storm sewer and a surface water sewer. There is no right of connection to a storm-water overflow sewer under section 106 of the Water Industry Act. These are normally the pipe line that discharges to a watercourse, downstream of a combined sewer overflow. It takes the excess flow from a combined sewer. A surface water sewer conveys rainwater; legally there is a right of connection for rainwater to this public sewer. A public storm water sewer can discharge to a public surface water, but not the other way around, without a legal change in sewer status by the water company. History Combined sewer systems were common when urban sewerage systems were first developed, in the late 19th and early 20th centuries. Society and culture The image of the sewer recurs in European culture as they were often used as hiding places or routes of escape by the scorned or the hunted, including partisans and resistance fighters in World War II. Fighting erupted in the sewers during the Battle of Stalingrad. The only survivors from the Warsaw Uprising and Warsaw Ghetto made their final escape through city sewers. Some have commented that the engravings of imaginary prisons by Piranesi were inspired by the Cloaca Maxima, one of the world's earliest sewers. In fiction The theme of traveling through, hiding, or even residing in combined sewers is a common plot device in media. Famous examples of sewer dwelling are the Teenage Mutant Ninja Turtles, Stephen King's It, Les Misérables, The Third Man, Ladyhawke, Mimic, The Phantom of the Opera, Beauty and the Beast, and Jet Set Radio Future. The Todd Strasser novel Y2K-9: the Dog Who Saved the World is centered on a dog thwarting terroristic threats to electronically sabotage American sewage treatment plants. Sewer alligators A well-known urban legend, the sewer alligator, is that of giant alligators or crocodiles residing in combined sewers, especially of major metropolitan areas. Two public sculptures in New York depict an alligator dragging a hapless victim into a manhole. Alligators have been