Metal water pipe bonding exists so that the plumbing in a house cannot sit at a hazardous voltage if something energises it. Using a buried metal water pipe as a grounding electrode is a separate requirement with a separate purpose. Both may apply to the same pipe, and confusing them leads people to remove one while believing the other still covers it.
Two requirements, one pipe
Where a metal underground water pipe is in direct contact with earth for a sufficient length, it is generally required to be used as a grounding electrode, connected near the point it enters the building and supplemented by an additional electrode. Separately, the interior metal water piping system is required to be bonded to the service equipment, the grounded conductor or the grounding electrode system. The first is about connecting the electrical system to earth. The second is about making sure conductive plumbing cannot become a shock source. A single conductor can sometimes satisfy both, which is exactly why people conflate them.
Why bonding the plumbing matters
Metal plumbing runs through every room of a house and is touched by people who are wet and barefoot. If a fault or a stray connection energises a pipe, the pipe becomes a large accessible conductor at a hazardous potential. Bonding ties the piping to the grounded system so it stays at the same potential and so that a fault which reaches the pipe produces enough current to open the protective device. This is also why an appliance that happens to be connected to the plumbing, like a water heater or a dishwasher, is not a substitute for a proper bonding conductor.
Plastic repairs break the path silently
The most common way this protection disappears is a plumbing repair. A section of copper replaced with plastic, a dielectric union installed to separate dissimilar metals, or a water meter swapped out all introduce a non-conductive break. The bonding path on the far side of that break is now floating. Wiring rules address the meter case specifically by requiring a bonding jumper around equipment likely to be removed, which is why you see a copper conductor looped around water meters. Nobody requires the plumber to jumper a repair coupling, which is why the electrical inspection of an older house should include a look at the plumbing.
Where the connection has to be made
When a metal water pipe is used as a grounding electrode, the connection point is specified to be near the entrance to the building, because that is the portion whose contact with earth is known. Connecting further along the interior piping does not qualify as the electrode connection, and it also risks depending on sections that could later be replaced. Connections must be accessible, and clamps must be listed for the purpose and suitable for the pipe material. The supplemental electrode requirement applies because a water pipe electrode can be compromised by future plumbing work in a way a driven rod or concrete-encased electrode cannot.
Gas piping and other metal systems
Interior metal gas piping is also required to be bonded, and the usual means is through the equipment grounding conductor of the circuit that supplies equipment likely to energise the piping, such as a furnace. Corrugated stainless steel tubing has additional bonding requirements from the manufacturer and from other codes, and those are stricter than many people expect because of lightning-related failures. Other metal piping systems and structural metal likely to become energised have bonding requirements too. The consistent principle is that any large accessible conductive system in a building should be tied to the grounded system rather than left floating.
What to check before you act
- Distinguish the electrode connection near the service from interior piping bonding.
- Check for plastic repairs or dielectric unions that break the bonding path.
- Confirm a bonding jumper spans the water meter and any removable equipment.
- Use clamps listed for the purpose and suitable for the pipe material.
Common questions
My house has plastic supply piping. Do I still need bonding?
If the interior piping is non-metallic there is nothing conductive to bond, but any metal piping sections likely to become energised still require bonding. Check what is actually installed.
Can the water pipe be my only grounding electrode?
No. Where a water pipe electrode is used it must be supplemented by an additional electrode, because plumbing changes can compromise it.
The practical takeaway
Bonding stops the plumbing becoming a shock hazard; the electrode connection ties the system to earth. Both can involve the same pipe and neither replaces the other, so check after any plumbing work that the conductive path you were relying on still exists.
References and further reading
- OSHA: grounding and bonding requirements for electrical systems
- NFPA: National Electrical Code overview covering bonding of metal piping systems
- CPSC: home electrical safety guidance including shock hazards around plumbing
Numerical scenarios are illustrative unless identified otherwise. Follow the exact product instructions; component ratings and local installation requirements can differ.
