A homeowner will probably only use Red pipe (Type M) or Blue pipe (Type L).

Red pipe is meant only for heating lines in a hot water heat system and may have some other uses. It cannot be used for house plumbing (domestic water). Red should be less expensive because the wall thickness is less than L

Blue pipe is meant only for domestic water, cold and hot and some other uses and can also be used in heating systems.

The fittings for both types of pipe are the same.

As far as I know, brand name copper pipe is made to uniform standards no matter where it's sold. So are fittings.

Your project will almost certainly be L pipe used with the new, no-lead solders.

I don't know that there's anything that restricts Type M pipe to the uses baymee states. Plenty of plumbers out there (including mine during our remodel) are running whole systems out of Type M copper. Why? Because it's significantly cheaper. May not last as long but then you get what you pay for.

The pipe is sized based on outside diameter (OD) and thus the fittings are the same for either pipe wall thickness. I hadn't noticed the red/blue labels at HD, but you will see the Type L or Type M designation printed on the pipe wall.

I have looked at my pipes and they all seem to be red. They have a red line on them. Thull, you say red(M) may not last as long. I don't plan on ever moving. What is the life expectency for the red and blue pipe? A lot of my pipes now have green corrosion on them. Should I be concerned about this? Thanks.

What is the acidity of your water? Green on the exterior of a pipe is caused by not wiping off the flux. Green on the inside is caused by acidic water.

For maximum durability, use Type L. And if you have acidic water, figure 20 years max for pinholes to occur.

Type M for plumbing is unknown in this area, so I did some Googling and sure enough, it's used.

Copper will pipes will last almost forever in normal water conditions. However if your water has a high acid level they could last 5 years.

Both the Uniform Plumbing code (UPC) and the International Residential Code (IRC) list Hard Drwan (rigid lengths) and Annealed (roll copper in types K,L & M as suitable for both residential supply & distribution piping.

Under the UPC type M (thin wall) may only be used for distribution within the structure if the line is at least 6" above grade. Distribution lines below grade (under slab) must be type L or K and all joints MUST BE brazed rather than soldered. The easy solution is to use continuous roll copper under slab so there is no joints.

Thank you everyone for responding. The green on my pipes is on the outside at the joints, so it must be the flux thing. Is that going to be an issue? I don't know if my water is acidic. I have well water with a softener. When tested, the guy said at the kitchen faucet it is perfect. If I were to switch over to the plastic water lines for my bathroom remodel job, could I expect a longer lifespan out of the plastic then out of the copper? It sure would be easier to use the plastic pipe. Please let me know if this is a good idea or not. Thanks again for all the great responses.

I checked the price for 1/2" L and M copper at the Despot. $8.35 vs. $12 for 10'. Not much price difference for a small job. I just installed a new tub and used one length. Hardly worth thinking about.