The sewer is a covered channel that carries human waste and stormwater away from inhabited areas, found as early as around 2500 BCE in the brick drains of Indus Valley cities such as Mohenjo-daro and later in Rome's Cloaca Maxima. After centuries of decline, the principle was revived at scale in the 19th century, most famously in Joseph Bazalgette's London system built from 1859 after the cholera outbreaks and the Great Stink of 1858. Modern systems separated foul drainage from drinking water and discharged it well away from the population.
Removing waste from the streets and water supply was foundational to public health and made dense living survivable. The 19th-century sanitary sewer broke the transmission of waterborne cholera and typhoid and underwrote the growth of the industrial city.