Quick Answer:

Short, random pressure dips usually come from something switching on and pulling down supply pressure, a failing pressure-reducing valve (PRV), or a utility-side sag. Start by logging when drops happen and what appliances or systems run then; fit a simple pressure gauge to an outdoor hose bib and watch it during a drop. If the swings are sharp and repeatable, suspect PRV instability or utility pressure sag. If the house has a smart shutoff or automation, check its event log for coincident activity. If you can’t isolate the cause, call a plumber or your water utility.

Why This Happens

Common reasons for intermittent whole-house pressure drops:

• High simultaneous demand: irrigation systems, laundry, and dishwashers can briefly pull the system down when they cycle.
• PRV problems: a worn or dirty PRV can open and close erratically, causing quick swings in delivered pressure.
• Utility-side issues: low mains pressure or a failing regulator on the street can cause brief sags during peak demand.
• Controls and smart devices: a smart shutoff or controller cycling valves can change pressure; check device logs to see timing and events.

If you see a pattern where pressure seems to drop during predictable cycles, or you notice the sequence “strong then weak then back,” it can point to an appliance or scheduled system. If pressure behavior looks like Pressure slowly builds then collapses, that pattern suggests volume filling then a valve or regulator letting go suddenly.

Step-by-Step What to Do

1. Start a simple pressure log

• Write down date and exact time of each drop. Note what was running in the house: sprinklers, washing machine, dishwasher, showers, water softener backwash, etc.
• Keep the log for several days to a week to find patterns (time of day, weekday vs. weekend).

2. Correlate with likely loads

• Compare the times in your log to irrigation schedules, laundry/dish cycles, and any scheduled backwashes on softeners or filters.
• Ask neighbors if they saw pressure changes at the same time — that helps tell if the utility is involved.

3. Put a gauge on a hose bib and watch during a drop

• Use a basic threaded pressure gauge on an easily accessible outdoor hose bib. Watch or record the gauge during an expected drop window.
• This confirms whether the true supply pressure is changing (gauge drops) or the issue is inside the house downstream of the gauge.

4. Check smart shutoff or automation logs

• If your home has a smart shutoff, irrigation controller, or connected valve, review its event log for valve openings/closures at drop times.
• Disable or manually override one system at a time to see if the drops stop — start with irrigation or any scheduled appliance.

5. Evaluate the pattern to suspect PRV vs. utility

• Sharp, frequent swings that happen even when internal valves are closed point to a failing PRV or utility regulator.
• If the gauge drops across the whole street or multiple homes report the same times, the utility is likely responsible.

6. Test isolation and temporary fixes

• Turn off the main shutoff to the house briefly and note whether the gauge holds at the street pressure (if you have access) or falls to zero inside. That helps isolate upstream vs. downstream problems.
• A temporary pressure tank or a replacement gauge won’t fix an unstable PRV or utility issue but can help diagnose.

What Not to Do

• Don’t live with random drops—pressure swings shorten the life of heaters, washers, and icemakers.
• Don’t randomly adjust the PRV if you’re not experienced; incorrect adjustments can cause consistently high pressure or damage plumbing.
• Don’t assume a single appliance is the cause without logging and testing; chasing the wrong item wastes time and can miss a larger issue.

When to Call a Professional

• Call a plumber if pressure drops continue after you’ve logged events and tested with a gauge, or if the PRV looks or sounds like it is cycling rapidly.
• Contact the water utility if multiple homes are affected or if your plumbing professional recommends a utility-side check.
• If pressure drops cause appliance errors (water heater shutdowns, washer faults, frequent icemaker failures) or you suspect a failing PRV, get professional help promptly. Also review the possibility that work on the system might have caused issues—see the note on post-repair problems if pressure began after service and the house shows symptoms like Water stops working after plumbing repair.

Safety Notes

• Turn off the main water before working on internal valves or replacing a PRV. Open faucets to relieve residual pressure first.
• Don’t try to remove or extensively adjust a PRV or meter-owned equipment — the utility or a licensed plumber should handle meter-side or regulated devices.
• If you smell gas or suspect a gas-fired water heater is affected by pressure swings, stop using the appliance and call a professional immediately.

Common Homeowner Questions

• Why does my pressure drop only at night? Often irrigation, timed softener backwashes, or utility demand patterns happen at night; use a log to correlate.
• Will a new PRV fix random drops? If the PRV is the cause (diagnosed by gauge testing and isolation), replacing or servicing it usually fixes unstable swings.
• Can the water company fix this? Yes, if multiple homes are affected or if the problem is upstream of your meter; contact them after you collect your log and gauge readings.