Plumbing systems refers to the maze of piping necessary to move potable water and natural gas through the home. The term also describes the drains and vents needed for removing gray water and sewage waste away from your home.
Some time ago, perhaps during a terrible drought, or an ice age or something equally desperate, one of our clever ancestors came up with a good idea. He imagined having a stream running through his cave. That he thought would serve well to bring in fresh drinking water and flush out waste without all the effort of hauling buckets in and out. Especially since buckets had not yet been invented.
The idea worked well so long as the cave was up-stream from everyone, since sewage treatment plants had not yet been invented either. Life was rough in those days.
Since not every cave had a suitable stream running through it, our hominid wife demanded that her mate do a bit of remodeling to install one. Thus, the art of plumbing (as well as all construction) was born and continues to evolve as we speak.
Plumbing systems have evolved a lot since ancient times. These days a plumbing system requires a water meter or well (to replace the stream), pumps (to make sure the water flow is consistent), water and gas piping (to place the water/gas where we want it), fixtures (provide a place to use the water), fittings (allow us to turn the water/gas on and off), filters (to remove unwanted material from the water), water heaters (to adjust the temperature of the water) and drain, waste, vents and septic pipes (so we can safely live downstream from one another).
Behold, our clever hominid/inventor has become a plumber; trained, practiced and licensed by the State to install, service, repair and modify these systems.
Plumbing piping is buried within the structure of the home and is difficult to access for repairs once installed. Since, any error can be damaging and costly to repair it is critical that this work be done properly and durably from the beginning.
Medieval homeowners took quality work very seriously. Mistakes and failures often lead to execution of the installer. This forced the trades to improve and quality skyrocketed to high levels. Unfortunately, civilization began to creep in and the enforcement of standards became less severe. These quality levels were never to be seen again. The best skills of the trades once were soldering, pipefitting and neatness. These have been replaced by contract writing and finger pointing.