Repairs to Copper Pipe

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.