Galvanized pipe is rarely used in residential water systems nowadays, although you may still find it in many homes. It tends to corrode, discoloring your water, and repair costs tend to be high. Galvanized is the most rigid material in use as water supply pipe, but rust builds up over time on the interior of the pipes. In situations where water freezes inside, these rusted pipes may burst as the frozen water expands and pushes against the metal walls.
PVC and Other Plastic
Plastic pipe is popular because it is lightweight and typically cheaper than copper or galvanized pipe. Some types of plastic pipe are used in underground applications because they’re not as likely to burst if the water inside freezes, as some metals will do. The most commonly used plastic pipe for residential water supply is polyethylene, or PE, because it is flexible and strong. It can be cut with a sharp knife or hacksaw and is ideal for both hot and cold water systems. Polybutylene, or PB pipe, and polyethylene tubing, or PEX, are the only other flexible plastic pipes that can be used with hot and cold water supplies. Polyvinyl chloride, also called PVC, is chemical-resistant and strong but is typically only used for cold water supplies.
Copper pipe is manufactured in four grades or thicknesses intended for residential plumbing use. Type K is the heaviest and most often used in general residential plumbing applications. Type L is slightly thinner-walled than K, and more commonly used for water lines than any other type of copper. Both types are available in both rigid and flexible pipes, making them versatile and easy to install in almost any plumbing situation. Type M is only manufactured as rigid pipe and is very light. It is recommended for light-duty residential water supply systems, but may not be allowed by some local building codes. Type DWV is very thin-walled and is also only available in rigid pipe. It is used for drainage, waste and vent, and not for water supplies. All copper is resistant to corrosion and expands somewhat to resist bursting in extreme temperatures.
The Best Material
The best material for residential water supply lines depends on the application. Copper pipe is widely used by professionals in most applications but some knowledge of plumbing is required to install it because of the use of soldering compounds and various fittings needed to join sections of pipe. Where the water has a pH below 6.5, copper can leach from your pipes into your drinking water, so it can’t be used in these types of water systems. Instead, PVC or PEX piping is often used because there is no risk of contaminants getting into your water. Galvanized is rarely used, but in most cases is installed outside the home. The potential for rust buildup makes galvanized pipe a costly water supply choice, but in underground or soil pipe installations, it is the strongest material overall.