Plumbing pipe materials: copper types and plastic types compared

One-line orientation

Pipe material selection is driven by application (supply vs drainage), water temperature, chemistry, and burial depth — the exam tests which copper grade or plastic type belongs to which use.

Key points

• Selection criteria: pipe material is chosen based on water chemistry (acidity, mineral content) to prevent corrosion, and on the application (supply vs drainage vs vent vs underground).
• Metal pipes:
  • Galvanized steel — zinc-coated steel used in older supply systems; the coating eventually corrodes and the steel rusts, restricting flow. Higher friction than copper or plastic increases pumping energy costs.
  • Copper Type K — thickest wall; specified for underground water supply.
  • Copper Type L — most common for interior water supply (hot and cold); balance of wall thickness and cost.
  • Copper Type M — thinnest supply-grade wall; suitable for low-pressure applications.
  • Copper Type DWV — specifically for drainage, waste, and vent (not a supply grade).
• Plastic pipes (generally lower friction than metal):
  • ABS (Acrylonitrile Butadiene Styrene) — lightweight; used for drainage and vent piping.
  • PE (Polyethylene) — flexible; used for cold water service, underground water service, and gas distribution; do not use plain PE as the main hot-water supply answer.
  • PEX (Cross-linked Polyethylene) — flexible; used for hot and cold potable supply and hydronic/radiant applications.
  • PVC (Polyvinyl Chloride) — durable, corrosion-resistant; widely used for cold water supply and drainage.
  • CPVC (Chlorinated Polyvinyl Chloride) — used for hot and cold potable supply. Its allowable temperature, pressure, and chemical exposure depend on the listed product.
• Insulation:
  • Hot water pipes — insulated to preserve heat.
  • Cold water pipes — insulated to prevent condensation and preserve coolness.

Copper grades (wall thickness) + plastic pipe by use

Copper wall thickness ranks K > L > M > DWV: K underground, L interior supply (most common), M low-pressure, DWV drainage only.

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Plastics: PEX / CPVC hot and cold, PVC cold and drain, ABS drain-waste-vent, PE cold, underground and gas. Galvanized steel is the one to avoid on new supply work — its zinc coating eventually corrodes from the inside, and the rough scale that follows chokes flow.

Confusions / comparison

Material	Hot supply	Cold supply	Drainage / vent	Underground	Notes
Galvanized steel	○	●	–	●	Zinc eventually corrodes; older systems
Copper K	–	–	–	●	Thickest common copper tube; often used underground or where greater strength is needed
Copper L	●	●	–	–	Most common interior supply
Copper M	●	●	–	–	Thinnest supply grade; low-pressure only
Copper DWV	–	–	●	–	Drainage/vent; not supply
ABS	–	–	●	–	Plastic DWV; lightweight
PE	–	●	–	●	Flexible; water service/gas distribution
PEX	●	●	–	–	Flexible hot/cold supply
PVC	–	●	●	●	Cold supply + drainage; not hot
CPVC	●	●	–	–	Hot/cold use; confirm the listed product’s limits

Related

→ Plumbing: water pressure & supply (pipe sizing, PSI) · DWV traps & vents (drainage pipe system context) · valves (isolation and backflow, often on copper L supply lines).