There are four basic types of copper tubing including type "M", type "K", “DWV,” and type "L" copper tubing. There are some building codes which require the use of a specific type of tubing, so it is important to know when to use M, K, DWV, or type L copper tubing. DWV has yellow lettering. Type M has red lettering, type K has green, and type L has blue.
Type M tubing is the most common type of plumbing pipe and is used for running water between the service line, hot water heater, and to the fixtures. ¾-inch type M tubing is used to run water from the main line, and ½-inch tubing is used to run water to the fixtures.
Type K is the thickest type of tubing, and is used for main water lines, vacuum pump lines, and underground water lines.
DWV is used mostly in commercial applications today such as bar and restaurant drains. However it is found in some older houses.
Type L copper is perhaps the most versatile as it is used and approved for more things than the others. It comes in “hard” and “soft.” Soft tubing is preferred for repair work, since it can maneuver around obstacles, but hard tubing is more durable and will stay in place. It is used for water inside and outside the home. It is often used outside the home, where it will be directly exposed.