Cast Iron - Used primarily in homes built before 1950, this is very heavy piping. Cast iron may rust or corrode, resulting in low water pressure and/or leaks if not properly maintained.
Galvanized Steel is used for all residential piping below the frost line (usually 4-6 feet deep) because it's relatively inexpensive. However, rust and corrosion can compromise galvanized steel over time, resulting in low water pressure and/or leaks.
Copper - This is the most common choice in homes today for plumbing supply and drain-waste-vent (DWV) systems. Copper is relatively expensive but has excellent longevity without significant corrosion or rust issues.
PVC - This plastic piping material lacks the longevity of copper but is cost-effective and not susceptible to corrosion or rust. PVC is recommended only for drain lines, not supply lines.