An elbow is a pipe fitting installed between two lengths of pipe or tubing to allow a change of direction, usually a 90° or 45° angle, though 22.5° elbows are also made.
The ends may be machined for butt welding, threaded (usually female), or socketed, etc.
It is used to change the direction in piping and is also sometimes called a "quarter bend".A 90 degree elbow attaches readily to plastic, copper, cast iron, steel and lead.
The main application of an elbow (90 degree) is to connect hoses to valves, water pressure pumps, and deck drains.These elbows can be made from tough nylon material or NPT thread.Źródło: https://en.wikipedia.org/wiki/Piping_and_plumbing_fitting
Water systems of ancient times relied on gravity for the supply of water, using pipes or channels usually made of clay, lead, bamboo, wood, or stone.Hollowed wooden logs wrapped in steel banding were used for plumbing pipes, particularly water mains.
US cities began using hollowed logs in the late 1700s through the 1800s.8 Today, most plumbing supply pipe is made out of steel, copper, and plastic; most waste (also known as "soil")11 out of steel, copper, plastic, and cast iron.11 The straight sections of plumbing systems are called "pipes" or "tubes".
Pipe normally has thicker walls and may be threaded or welded, while tubing is thinner-walled and requires special joining techniques such as brazing, compression fitting, crimping, or for plastics, solvent welding.
These joining techniques are discussed in more detail in the piping and plumbing fittings article.Źródło: https://en.wikipedia.org/wiki/Plumbing#Materials
Water supply and sanitation has been a primary logistical challenge since the dawn of civilization. Where water resources or infrastructure or sanitation systems are insufficient for the population, people fall prey to disease, dehydration, and in extreme cases, death. Major human settlements could initially develop only where fresh surface water was plentiful, such as near major rivers. Over the millennia, technology has dramatically increased the distances across which water can be relocated, but the availability of clean and fresh water remains a limiting factor on the size and density of population centers, and is expected to remain so into the foreseeable future.Źródło: https://en.wikipedia.org/wiki/History_of_water_supply_and_sanitation.