You know how some pipes are made of copper well what makes copper good for making pipes?
Aluminum profiles are extruded, in simple terms Aluminum when heated to a certain state is pushed through a hole of the shape that you require and out pops your window frame profile or whatever, in theory this can be done to an infinate length Copper pipe is similar, but it is forced thorough a die which has spokes to support the central die, i believe as the copper is parted to go around the central die it is still maleable enough to fuse together on the other side, if you can picture that you are doing well!!
Some of the answers here are getting to the right point, but notice, copper is primarily used for potable water in your house. It is not strong, comparatively, you rarely see copper pipe above 2-3 inches. It is workable, and relatively soft, has reasonable corrosion resistance, although it will corrode (hence the EPA's lead and copper rule). Per unit weight, it is VERY expensive. Virtually all of the water mains of any size are ductile iron. But one of the main reasons it is used in domestic water distribution is that copper has natural inhibitive properties for biological growth. Think about it...Water will always be flowing in the main past your house, but your water service can reside in the pipe for weeks, partiularly if you go away for awhile, etc. But notice that the water is generally devoid of turbidity or bacteria. You can drink the water safely even though it has been sitting around in the pipes.
Easy to maneuver, fairly bendable (up to 3 degree's at a min of 300', that's actually very good), chemical wise it is safe with water (wont rust, wont chip, water is drinkable when it goes through it), compared to other metals it's cheap. Copper is becoming more expensive compared to plastics and other mostly man made things so they are switching to something that's closer to plastic. Something more common is High Density Poly Ethel (HDPE). It's what just about everyone has switched to. Worked for a civil engineering place as a drafter (had to look up material costs).
Copper has a number of useful characteristics that make it good for plumbing: It is malleable, meainging that the pipes can easily be bent to fit into the available space. If is not soluble in water, meaning that copper won't leach into the drinking water. Copper, as well as several other metals, exhibits an oligodynamic effect which acts to kill single celled organisms that come into contact with it. This means that copper won't support the growth of fungus or mold from standing water within the pipes.
