What are the different types of copper pipe (K, L, M)?

All three types are made to one standard, ASTM B88, the specification for copper water tube. ASTM says the right type for a given job "is determined by the internal or external fluid pressure, by the installation and service conditions, and by local requirements." So the standard does not rank the types as good, better and best. It gives you three wall thicknesses and leaves the choice to the designer and the code.

Here is how the three compare on the two sizes you see most in houses. The wall figures are nominal, in inches, from the CDA handbook's dimension tables.

Sizes are nominal, so a "1/2 inch" pipe measures 5/8 inch across the outside. Type M is not sold in the soft temper at all. And the color codes are not paint jobs: CDA says hard tube has the type information printed on it in a color that identifies the type.

### Hard copper, soft copper, and what temper means

Every copper tube also has a temper, which is how hard the metal is. CDA explains that in the piping trades drawn temper tube is often called hard tube and annealed tube is called soft tube.

Tube selection and joint selection are separate checks; compare press fittings versus solder for a copper repair.

• Hard (drawn) copper comes in stiff straight sticks. Direction changes can use compatible fittings, but CDA says both drawn and annealed tube can also be bent with appropriate equipment. Table 4.1 distinguishes tube size, type and temper; its listed radii are minimums for mechanical bending equipment only. The hand bender pictured in Figure 4.1 is for annealed tube only, and the selected tool’s instructions still apply. It is what you see running along a wall or through an attic.
• Soft (annealed) copper comes in coils and bends by hand. It can be joined with soldered fittings, flare fittings or compression fittings. Fewer joints make it handy for buried runs and tight retrofits.

CDA notes that annealed tube can withstand the expansion of freezing water several times before bursting, though it adds that this does not mean copper water lines should be subjected to freezing.

The CDA table lists K, L and M for domestic water service and distribution. On paper, any of them can carry drinking water. Where they differ is in how the industry and the codes use them.

• Type K has the most metal in the wall and is sold in both tempers. Its wall is the reason it gets picked for buried or hard-working runs. The CDA table also lists K for natural gas, fuel oil and compressed air, as it does for L. (Gas piping is its own code topic. See our page on gas line pressure tests.)
• Type L is the middle wall, also sold in both tempers. It is the common step up from M and the weight some codes name as the minimum for water piping (more on that below).
• Type M is the thin-wall option and is made only as hard tube. That is why you never see it in a coil.
• DWV is not for pressure water. It is drain, waste and vent pipe, made in larger sizes and thinner still. Copper drains are rare in newer homes. See cast iron drain pipe lifespan for what older Phoenix drain lines are usually made of.

CDA's own handbook recommends Type M for water distribution systems above and below ground, and Type M hard for buried service in straight lengths. It also says plainly that "Plumbing and mechanical codes govern what types may be used." That leads to the code question.

### Is Type M allowed in Phoenix?

Phoenix's own amendments do not restrict copper type, but the base code text matters.

Phoenix adopted the 2024 Phoenix Building Construction Code under Ordinance G-7397, effective August 1, 2025. Its amendments to the Uniform Plumbing Code (UPC) and the International Plumbing Code (IPC) do not change the copper tube provisions. The one water-pipe amendment we found in the UPC set says non-metallic potable water pipe, fittings and valves shall not be exposed in exterior outdoor locations, which is a sun and heat rule, not a copper-type rule.

The adopted base code also matters. Phoenix's IPC water-pipe tables list copper tube types K, WK, L, WL, M and WM. The city also publishes UPC amendments, but those amendments alone do not reproduce the base UPC copper requirements. We have not verified the applicable 2024 UPC Type M conditions here. Ask the Phoenix permit office which adopted code and section govern the job before selecting Type M, particularly for concealed or buried runs. A different state's code is not proof of what Phoenix permits.

You can usually identify your copper in two minutes.

1. 1Find a bare run of pipe. Under a kitchen sink, near the water heater, in the garage, or in the attic are the usual spots.
2. 2Wipe off dust and look for printing along the tube. On hard copper, CDA says the information is printed in the type's color, and the tube must also carry incised markings showing "tube type, the name or trademark of the manufacturer, and the country of origin."
3. 3Look for the letter: K, L, M or DWV, along with ASTM B88 (or B306 for DWV).
4. 4If the printing has faded or the pipe is behind a wall, you can still guess from age and size, but the stamp is the only real answer. A plumber with a camera or an access panel can check without opening drywall.

Here is the practical takeaway.

• The letter is not a quality grade. M is not "bad" pipe. A thinner wall means less metal, but CDA's list of the usual causes of copper corrosion problems includes excessive flow velocity or turbulence, poor workmanship, aggressive flux, and aggressive water or soil. Those matter more to a pipe's life than the letter. For the full picture on how long the pipe lasts, see how long old pipes last before they fail and pinhole leaks in copper pipes.
• Age matters more than type. EPA says lead pipes are more likely in homes built before 1986, and it names plumbing with lead solder as the most common problem in homes without lead service lines. If your copper house is from that era, consider a lead test.
• Repairs and additions. K, L and M share the same outside diameters for a given size, so they take the same fittings. Ask the plumber which type they are using and why. The capillary solder joint entry explains the separate soldered-connection mechanism; matching outside size does not finish the joint specification.
• Copper versus plastic. Weighing copper against PEX for a repipe? See what drives repipe cost, PEX vs copper.

HQ Plumbing & Air is licensed and insured, gives free estimates, and quotes the price up front before any copper repair or repipe starts. If you find a stamp you cannot read or green crust at a joint, that is worth a look.