Galvanized steel potable water supply and distribution pipes are commonly found with nominal pipe sizes from 3⁄8 inch (9.5 mm) to 2 inches (51 mm). It is rarely used today for new construction residential plumbing. Steel pipe has National Pipe Thread (NPT) standard tapered male threads, which connect with female tapered threads on elbows, tees, couplers, valves, and other fittings. Galvanized steel (often known simply as "galv" or "iron" in the plumbing trade) is relatively expensive, and difficult to work with due to weight and requirement of a pipe threader. It remains in common use for repair of existing "galv" systems and to satisfy building code non-combustibility requirements typically found in hotels, apartment buildings and other commercial applications. It is also extremely durable and resistant to mechanical abuse. Black lacquered steel pipe is the most widely used pipe material for fire sprinklers and natural gas.
Let's start with the easiest possible project: Installing a new shower head is as simple as it gets. Typically, all you have to do is unscrew the old shower head from the shower arm (the pipe coming out of the wall), clean off the threads on the shower arm and wrap a bit of Teflon tape around it, then screw on the new shower head. It's really that simple (and if you don't believe me, check out the video above from Dummies.com). Do read the installation instructions on the shower head you buy, though. Some are designed not to require Teflon tape and can actually leak if you use it.
As with other construction workers, employment of plumbers, pipefitters, and steamfitters is sensitive to fluctuations in the economy. On the one hand, workers may experience periods of unemployment when the overall level of construction falls. On the other hand, shortages of workers may occur in some areas during peak periods of building activity.
Plumbing originated during ancient civilizations such as the Greek, Roman, Persian, Indian, and Chinese cities as they developed public baths and needed to provide potable water and wastewater removal, for larger numbers of people. Standardized earthen plumbing pipes with broad flanges making use of asphalt for preventing leakages appeared in the urban settlements of the Indus Valley Civilization by 2700 BC. The Romans used lead pipe inscriptions to prevent water theft. The word "plumber" dates from the Roman Empire. The Latin for lead is plumbum. Roman roofs used lead in conduits and drain pipes and some were also covered with lead. Lead was also used for piping and for making baths.