What do the plumbing work?
Hydraulics is a fairly complex area and not everyone can be found in it. In such matters require specialized knowledge and skills, and such work is also associated with great responsibility, because the slightest error can result in a major accident. Plumbing may involve many issues. Sometimes it will be installation of hydraulic, other times repairing the broken pipe or replace gaskets and scope of such work is very extensive. Specialists in the field of hydraulics are needed in each region, because each building are installed plumbing. So it is very important work, without which it would be hard for us to get around.
Wikipedia facts
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
Something about plastic pipes
Plastic pipe is a tubular section, or hollow cylinder, made of plastic. It is usually, but not necessarily, of circular cross-section, used mainly to convey substances which can flow ? liquids and gases (fluids), slurries, powders and masses of small solids. It can also be used for structural applications; hollow pipes are far stiffer per unit weight than solid members.
Plastic pipework is used for the conveyance of drinking water, waste water, chemicals, heating fluid and cooling fluids, foodstuffs, ultra-pure liquids, slurries, gases, compressed air and vacuum system applications.
Źródło: https://en.wikipedia.org/wiki/Plastic_pipework