If your bill jumped and nothing in your routine changed, you’re losing water somewhere. Average indoor use runs about 80-100 gallons per person per day. If your household’s usage is running 20%+ above your own historical average for the same season, that’s not noise — that’s a leak until proven otherwise.
Here’s the math that matters: a leak running at just 1/8″ diameter under typical household pressure can move over 4,000 gallons a day. You don’t need a burst pipe to see a huge bill — a leak too small to hear can still cost more than a rate hike.
Common Causes, Ranked by How Much Water They Actually Waste
1. Running Toilets — the #1 cause, and the most variable in severity
A worn flapper lets tank water bypass into the bowl continuously. Severity depends on the gap:
- Slow seep (flapper barely worn): 30-50 gallons/day — adds roughly $5-15/month depending on your rate.
- Steady leak (visibly worn flapper, won’t fully seat): 200+ gallons/day — this is the classic “silent” leak that can add $50-100+ to a monthly bill.
- Stuck-open flapper or failed fill valve: can run continuously at 2-4 gallons/minute, which is 2,880-5,760 gallons/day. This will spike a bill by hundreds of dollars in a single cycle and is usually caught by the utility before the customer notices.
Fill valve failures are different from flapper failures: if you hear water running constantly (not intermittently), the fill valve isn’t shutting off at the float level, and water is going out the overflow tube — same outcome, different parts to replace.
2. Hidden Pipe Leaks (Slab, Wall, Crawl Space)
A 1/16″ pinhole leak in a pressurized line (typical residential pressure: 40-80 psi) can discharge 1-2 gallons per minute — that’s 1,440-2,880 gallons per day, easily a $100-300+ bill spike depending on your local rate per CCF (hundred cubic feet, the standard billing unit — 1 CCF = 748 gallons).
Slab leaks specifically are deceptive because the slab and soil absorb the water before it surfaces. By the time you see staining or smell mildew, you’re often 30-60+ days into the leak. Copper pipe pinhole leaks from pitting corrosion and pipe joints failing from ground settling are the two most common slab-leak causes.
3. Water Heater Failures
- T&P (temperature and pressure) relief valve stuck open or weeping: can waste 1-3 gallons/minute when actively discharging — that’s potentially thousands of gallons in a day if it sticks open, though most weep intermittently and waste less (10-50 gal/day).
- Tank corrosion pinhole: usually slower, but constant — often 5-20 gal/day, rising over time as corrosion spreads.
- Anode rod fully depleted: doesn’t leak by itself, but accelerates tank corrosion that leads to the above. Anode rods typically need replacement every 3-5 years; skipping this is the single most common reason water heaters fail early in this region’s harder municipal water.
Tanks over 10 years old account for the large majority of heater-related leak calls we get. If yours is in that range and you haven’t replaced the anode rod, that’s your first move before anything else.
4. Irrigation System Leaks
A cracked irrigation line running during scheduled cycles can go completely unnoticed because the water disappears into landscaping. A single stuck zone valve that doesn’t fully close can run a zone 24/7 instead of for its scheduled 10-20 minutes — turning a normal $10/month irrigation cost into hundreds of dollars. If your irrigation controller shows zones running outside their schedule, or your summer bill is far higher than the same month last year with no change in irrigation schedule, check valves first.
5. Supply Line and Valve Drips
A drip from a worn supply line (under sinks, toilets, washing machines) typically wastes far less per incident — usually under 5 gallons/day per drip — but multiple aging lines throughout a house compound. A house with 8-10 supply lines all original to a 15+ year old build commonly has 2-3 weeping simultaneously, adding up to a real number over a billing cycle.
6. Water Softener/Filtration Malfunctions
A softener stuck in regeneration cycle, or with a failed bypass valve, can continuously drain to waste. This is typically 5-15 gallons per regeneration cycle under normal operation, but a stuck valve running continuously can hit hundreds of gallons per day. If your softener’s salt usage suddenly dropped (system is using less salt than normal) while your water bill rose, suspect a bypass or control valve failure.
7. High Static Pressure
Municipal supply pressure above 80 psi (check with a $10 gauge that threads onto an outdoor spigot) accelerates failure in every rubber and plastic component in your system — supply lines, washing machine hoses, toilet fill valves, water heater T&P valves. Pressure-related failures cluster together: if one component fails from pressure, expect others to follow within months. A pressure-reducing valve (PRV) set to 50-60 psi extends the life of everything downstream.
How to Find the Leak: Specific Tests, Specific Numbers
The Meter Test (most reliable, do this first)
- Shut off everything that uses water — including ice makers and any auto-fill (humidifiers, pool fill, water softener).
- Find your meter (curb box or yard box) and record the exact reading, including the smallest digit/dial.
- Wait exactly 2 hours with zero water use.
- Read again.
What the result means:
- No change at all: no active leak at the time of test (doesn’t rule out an intermittent leak, like a toilet that only runs after flushing).
- Small change (under 1-2 gallons in 2 hours): consistent with a slow supply line drip or minor toilet seep.
- Larger change: consistent with a running toilet or a pipe leak — move to isolation testing below.
Most meters also have a small triangular or star-shaped leak indicator dial that physically spins any time water is flowing anywhere downstream, even a trickle. Watch it for 60 seconds with everything off — if it’s moving at all, something is leaking right now.
Isolation Test (find which zone)
After confirming a leak with the meter test, shut off the main valve to your house, then turn it back on while keeping every fixture’s individual shutoff closed except one zone at a time (e.g., just the irrigation system, or just inside plumbing). Re-run the meter test for each zone. This narrows “somewhere in the house” down to “irrigation” vs. “inside plumbing” vs. “water heater” before you start opening walls.
Toilet Dye Test
Add food coloring directly to the tank (not the bowl), wait 15 minutes without flushing, check the bowl. Any color in the bowl confirms flapper bypass. Do this for every toilet in the house — multi-toilet households often find the leak isn’t where they expected.
Bill History Comparison
Pull 12-24 months of billed usage if your utility provides it online (most do). Compare the same calendar month year-over-year, not month-to-month, since usage is seasonal (irrigation in summer, more indoor water in winter for some households). A 20%+ jump in the same month vs. last year, with no household changes, is your threshold for “investigate now.”
Regional Factors Specific to the Pacific Northwest
- Galvanized and polybutylene supply lines: common in homes built before the mid-1980s (galvanized) and through the early 1990s (poly-B). Galvanized pipe corrodes from the inside, narrowing the pipe and eventually pitting through — this is a multi-decade process that often reaches failure right around the 40-50 year mark, which puts a lot of regional housing stock in the failure window now. Poly-B fittings fail at the crimped joints, not the pipe itself.
- Wet-season masking: regional rainfall keeps soil saturated much of the year, which hides outdoor and slab-edge leaks that would show as an obvious wet patch in a drier climate. If your winter bill is up but your yard “looks normal,” that’s not reassurance — saturated ground absorbs a leak’s output without visibly pooling.
- Freeze-thaw lag: a hard freeze can crack a pipe without an immediate leak, because the ice plug seals the crack. The leak shows up days to weeks later when temperatures rise and the plug melts — so a bill spike in February or March can be the delayed result of a freeze event from weeks earlier. Exposed crawl space lines and hose bibs without frost-free design are the most common failure points.
- Root intrusion: mature trees in older established neighborhoods send roots toward any consistent moisture source, including sewer lines and buried irrigation pipe. Root intrusion typically causes a slow leak that worsens over 1-3 years before becoming a clog or full break, so a gradually climbing bill over several billing cycles (rather than a sudden spike) fits this pattern.
- Municipal water hardness: harder water in much of the region accelerates anode rod depletion and tank-style water heater corrosion versus what manufacturers’ standard lifespan estimates assume, which is why the 10-12 year heater-failure window we cited above tends to land on the earlier end here.
When DIY Testing Isn’t Enough
Call a professional when:
- Meter test confirms a leak but isolation testing doesn’t pinpoint it
- You find warm spots on flooring (hot water slab leak) or unexplained foundation cracking
- Your home has galvanized or poly-B piping and you haven’t had it inspected
- Static pressure tests above 80 psi
- The leak is in a sewer or main line (root intrusion suspected)
Cascade Northwest Plumbing uses acoustic leak detection and thermal imaging to locate the exact leak point before any drywall or slab is opened — this is the difference between a targeted repair and a guess-and-check demolition.
Serving Your Neighborhood
We provide leak detection and repair services throughout:
- Portland and surrounding suburbs
- Vancouver, WA and surrounding suburbs
If your meter test confirms a leak you can’t isolate, contact Cascade Northwest Plumbing for a professional leak detection inspection.