Because of its durability, copper is the preferred material for most water supply lines. However, copper pipe can leak when dented, punctured, or weakened from corrosion. Joints can degrade too.
Even if you have galvanized or plastic supply pipe in your house, you may want to use a transition fitting and switch to copper when making a repair or extending a line. When joining copper pipe to steel pipe, be sure to use a dielectric fitting to avoid corrosion.
Type M copper pipe is fine for most residential work. Buy lead-free solder and flux paste.
Sweating a large copper drain line calls for a large propane torch; you're probably better off hiring a pro for such work.
Compression fittings require no special skills to install, but they are expensive. Use them only where they will be exposed; any joints hidden in a wall must be sweated.
An hour or two for most repairs
Groove-joint pliers, tubing cutter, hacksaw, multiuse wire brush, flux brush, propane torch, fiber shield
Using a pipe cutter, handling a propane torch
Shut off the water; drain the line; position a cookie sheet or protective shield to protect flammable surfaces
Copper pipe and fittings, flux, solder
Shut off the water. Use a tubing cutter to cut on each side of the damaged area. Screw the cutter tight, rotate it a full turn, tighten, and rotate again until the cut is complete. If there is not enough room, cut with a hacksaw. Exert gentle pressure to avoid flattening the pipe. File off burrs.
Ream and polish the pipe and couplings using a multiuse brush. Brush on flux and slide a coupling on each side, position the replacement piece, and slide the couplings back halfway. (To install a standard coupling or elbow, give it a slight twist as you push it all the way into place.)
Protect framing and nearby walls with a cookie sheet or fiber shield. Aim the torch so the tip of the blue flame touches the middle of the fitting. When the flux sizzles after 5 seconds or so, move the flame to the opposite side and heat it briefly. Touch solder to the joints.
Once solder has been sucked into the joint all around, wipe the joint with a rag to smooth the solder and eliminate any drips. Fold the rag several times and/or wear leather gloves. Repeat for the other side of the fitting. Check the work area an hour later to be sure nothing is smoldering.