High Quality Content by WIKIPEDIA articles! Tap water (running water, city water, municipal water, etc.) is potable water supplied to a tap (valve) inside the household or workplace. It is a principal component of "indoor plumbing", which became available in urban areas of the developed world during the last quarter of the 19th century, and common during the mid-20th century. The application of technologies involved in providing clean (potable) water to homes, businesses and public buildings is a major subfield of sanitary engineering. Calling potable water "tap water" distinguishes it from the other main types of potable water, such as water from rainwater-collecting cisterns, from village pumps (town pumps), or from streams, rivers, or lakes (whose potability varies).