Quick Answer:
If you see water sputtering or spitting only when you open the cold side of a tap, it is usually trapped air in the cold supply lines or a pressure/valve issue rather than the system actually losing water. Start by testing hot vs cold at the same fixture, then fully open a faucet to purge the line. If the problem repeats across fixtures or floors, a licensed plumber can trace the source and inspect pressure regulators and vents safely.
Why This Happens
Air can enter the plumbing system in several common ways: a recent main shutoff or municipal work, a pressure regulator (PRV) change, water heater refills, or a valve that allows a small air pocket to form. Because cold and hot lines follow different paths (cold straight from supply, hot through the water heater), the problem can show up on one side only. For problems that follow a recent adjustment, consider Air spitting after PRV adjustment as a likely clue. If you see the opposite pattern, refer to Air bursts only from hot side.
Step-by-Step What to Do
1. Confirm which side is affected
- Turn the handle to hot only, then to cold only, and observe. This tells you whether the issue is isolated to cold, hot, or both.
2. Open the faucet fully to purge air
- Open the affected cold tap fully (not just a trickle) for several minutes to let trapped air escape. Do this at the lowest level fixture first, then at higher fixtures if needed.
3. Note timing and recent events
- Record whether the spitting began after a water outage, municipal work, PRV adjustment, or after refilling or servicing the water heater. That history helps a plumber narrow the source.
4. Check upstairs vs downstairs behavior
- Test fixtures on different floors. If upstairs and downstairs behave differently, that points to where the air is entering or where pressure differences exist.
5. Observe whether the problem returns
- If purging clears it and it doesn’t come back, you likely removed trapped air. If it returns quickly or affects multiple fixtures/floors, stop and arrange for a pro to inspect valves, PRV, and vents.
What Not to Do
- Don’t keep cycling the main valve or dismantling cartridges; if air returns after purging or affects multiple floors, let a plumber inspect venting and supply components.
- Don’t use forceful or intrusive DIY fixes on pressurized components such as PRVs or sealed plumbing fixtures.
When to Call a Professional
Call a licensed plumber when:
- The air returns after you purge lines or the problem affects multiple fixtures or floors.
- You notice pressure fluctuations, banging (water hammer), or a drop in supply pressure beyond sputtering.
- The issue began after PRV work, a main shutoff, or you suspect a hidden leak or failed check valve. A plumber can safely trace the source, test the PRV and supply pressure, and inspect venting and shutoff assemblies.
Safety Notes
- Avoid working on pressurized components unless you know what you’re doing. Unexpected pressure can cause injury or water damage.
- Turn off the main only if you need to stop an active leak; repeated cycling can introduce more air or stress fittings.
- If you smell gas, see electrical sparking, or encounter other hazards while checking plumbing, leave the area and call the appropriate emergency services first.
Common Homeowner Questions
- Why did this start after the water was shut off? — Shutoffs let air into the pipes; opening faucets fully usually purges it.
- Is it dangerous if only cold sputters? — Not usually dangerous, but it can indicate pressure or valve issues that should be checked if persistent.
- Will a plumber need to dig up the line? — Most often no; plumbers use pressure tests and access points to trace air/pressure problems before any excavation.
For more related articles, see the Air Spitting From Faucets hub.