Most sudden spikes trace back to a leak or a change in household water use, and you can usually tell which one in under an hour. Start by running a meter no-use test and a toilet dye test today. If both come back clean, check your irrigation system and appliances next. If the meter still won’t sit still with everything off, that’s your sign to call a licensed plumber before the leak gets more expensive.

TL;DR:

  • The most common cause of high water bills is undetected leaks, especially in toilets, supply lines, or underground service lines, which can waste hundreds of gallons daily.
  • Using your water meter to conduct a leak test involves shutting off all water use and checking for movement or a leak indicator, with persistent movement indicating a hidden or service-line leak.
  • Toilet leaks are often caused by failing flappers or misadjusted fill valves, which can be confirmed through a simple dye test and fixed with affordable, quick DIY repairs.
  • Outdoor system faults, such as stuck sprinkler valves or pool autofill leaks, can significantly increase water use without obvious signs, requiring a manual inspection and schedule adjustments.
  • When DIY troubleshooting fails and the meter keeps moving with the main shutoff closed or if there is sewage odor or pooling water, calling a licensed plumber for professional leak detection is essential.

Table of Contents

Top Causes of a High Water Bill, Ranked by Likelihood

Not every cause deserves equal attention. Leaks come first because they’re both the most common and the most fixable once you find them.

Undetected leaks top the list every time. A running toilet alone can waste up to 200 gallons a day, and most homeowners never hear it happening. Supply line drips under sinks, a cracked pipe under the slab, or a failing service line between the meter and the house can all rack up usage silently for weeks.

Higher household use is the second most common explanation, and it’s easy to overlook. Houseguests, filling a kiddie pool, an extra lawn watering cycle during a heat wave, or a new pet’s water bowl habit can all nudge a bill upward without anything being broken.

Beyond those two, a handful of specific culprits show up again and again on utility troubleshooting pages:

  • Irrigation and sprinkler faults — a stuck valve, a cracked line, or a controller reprogrammed by a power outage
  • Appliance and water-heater problems — a failing supply line, a leaking tank, or a pool autofill valve stuck open
  • Water softener regeneration cycles — a softener stuck mid-cycle can run water continuously
  • Billing errors — estimated meter reads or a longer-than-usual billing period that makes usage look inflated

EPA WaterSense data shows toilets, clothes washers, and showers account for the largest share of indoor water use in a typical home, which is exactly why those fixtures deserve the first look when a bill jumps.

How to Use Your Water Meter to Check for a Leak

Your water meter is the single most reliable diagnostic tool you already own, and it costs nothing to use. Utilities like Austin Water recommend this exact process to customers calling in about a high bill.

  1. Find your meter — usually near the curb or property line in a small concrete box — and record the reading. Take a photo with your phone; it’s an easy way to avoid misreading tiny dial numbers later.
  2. Shut off every water-using fixture and appliance in the house for one to two hours. No dishwasher, no laundry, no hose running outside.
  3. Recheck the meter. If the reading changed at all, water moved somewhere while everything should have been off.
  4. Narrow the location. Shut off the main valve where the water line enters your house, then check the meter again. If it’s still moving with the main closed, the leak is between the meter and the shutoff, likely the service line itself.

Pro Tip: Many meters have a small triangular or star-shaped leak indicator that spins even at a trickle. Watch it for 30 seconds with everything off. If it’s moving, you have your answer without waiting the full hour.

If the meter keeps ticking after you’ve confirmed irrigation valves are closed and the main is shut, you’re likely dealing with a hidden or service-line leak that needs professional leak detection and possibly excavation to locate and fix.

Toilets: The Quiet Budget-Killer Behind Most High Bills

Inspecting toilet tank leak components

Toilets cause more mystery water bills than any other fixture in the house, and the reason is almost always one of two parts failing quietly. A worn flapper lets tank water seep into the bowl around the clock, while a misadjusted fill valve can let water trickle into the overflow tube nonstop, refilling itself in an endless loop nobody notices.

The dye test settles the question in minutes. Utility programs like Dublin San Ramon Services District’s leak-check resources recommend it, and some utilities even hand out free dye tabs.

  • Drop food coloring or a dye tab into the tank, not the bowl.
  • Wait 10 to 15 minutes without flushing.
  • Check the bowl. Any color that shows up means the flapper is leaking.

Most flapper replacements run under $15 in parts and take about ten minutes with basic tools. Adjusting the fill valve float to lower the water level is just as quick. If you replace the flapper and dye still shows up a week later, or the toilet keeps running after a fresh fill valve, it’s worth having a plumber look at the flush valve seat itself, since a scratched or warped seat won’t seal no matter what flapper you install.

Faucets, Appliances, and Water Heaters: Where Drips Add Up

A faucet that drips once per second wastes over 3,000 gallons a year, and that number climbs fast if the drip is happening somewhere you rarely look, like a laundry room supply valve or a refrigerator ice-maker line tucked behind the unit.

Walk through these spots when the meter test points indoors but toilets check out clean:

  • Under every sink — look for water stains, warped cabinet wood, or a faint musty smell
  • Behind the washing machine — supply line hoses degrade from the inside out and often fail without warning
  • Refrigerator ice-maker line — a slow pinhole leak here can run for months unnoticed
  • Water heater base — check for pooling water, rust streaks, or corrosion around the tank seams
  • Dishwasher — a failing door seal or supply connection can leak small amounts with every cycle

A worn supply line or a new flapper is a reasonable DIY swap for most homeowners. A leaking water heater tank, a cracked dishwasher inlet valve, or anything involving soldered copper connections is where it makes more sense to bring in a professional rather than risk water damage from a bad repair.

Outdoor Systems: Irrigation, Sprinklers, and Pool Autofill

Water pooling around irrigation valve

Outdoor water use is invisible in a way indoor use isn’t. Nobody notices a sprinkler head running an extra ten minutes a day, but over a billing cycle that adds up to real gallons.

Walk your yard looking for soggy patches that don’t match where you actually watered, sprinkler heads still spraying after the cycle should have ended, or a valve that never fully shuts. Check your irrigation controller too. Power outages and battery resets frequently revert programming to factory defaults, which sometimes means daily watering instead of twice a week.

  • Inspect each zone manually for stuck valves or broken heads
  • Confirm the controller’s schedule matches what you actually intended
  • Check pool autofill: normal evaporation loses about a quarter to half an inch of water per day; losing two inches or more per week points to a leak in the autofill line or pool shell
  • Reset irrigation timing seasonally rather than leaving summer schedules running into fall

Water Softeners and Water Heaters: Cycles and Slow Tank Leaks

A water softener uses water by design, during its regeneration or backwash cycle, but a softener stuck in that cycle can run continuously and mimic a leak on your bill. Check the drain line for unexpected discharge, and listen for a softener that’s still cycling long after it should have finished.

Water heaters fail differently. Look for a wet floor around the base, rust streaks down the tank, or water discharging from the temperature-and-pressure relief valve, all signs the tank itself may be failing rather than just running long.

  • Manually advance or reset a stuck softener cycle to stop the water flow temporarily
  • Schedule softener service if it cycles more than once every few days without explanation
  • Treat any water heater leak as a call-a-plumber situation, since a failing tank rarely fixes itself

Could This Just Be a Billing Mistake?

Before you tear apart your plumbing, pull your last few bills and compare. Utilities make mistakes too, and it’s worth ruling that out first.

Line up the current bill against the same period last year. If usage is dramatically higher with no obvious explanation, check the number of billing days on each statement. A 35-day cycle will naturally show more usage than a 28-day one, and that difference alone can look like a spike when it isn’t.

  • Look for the word “estimated” on your previous bill. If a meter reader couldn’t access your meter, the utility estimates usage, then corrects it on the next actual reading, sometimes producing a large one-time jump.
  • If you’ve already repaired a confirmed leak, ask about a leak adjustment or bill credit. Portland Water Bureau and many utilities nationwide offer this, typically requiring proof of repair within about 90 days of the leak being found.
  • Gather a plumber’s receipt, replaced parts, or photos of the repair before calling.
  • When you call customer service, ask directly: “Was this bill estimated or actual? Can you confirm my billing period length? Do you offer a leak adjustment, and what’s the deadline to apply?”

When to Call a Plumber Instead of Troubleshooting Further

DIY testing covers most cases, but a few signals mean it’s time to stop guessing and bring in a professional. If the meter keeps moving with the main shutoff closed, if you smell sewage or see water pooling near the foundation, or if you’ve already fixed the obvious suspects and the bill is still high, you’re likely looking at a hidden or service-line leak.

A licensed plumber’s diagnostic process usually includes a meter pressure test, electronic leak detection equipment to pinpoint the sound of escaping water, and sometimes a camera inspection of buried lines before any digging starts. Pricing shapes vary by what’s found: a diagnostic visit is typically a flat fee, a supply-line repair costs less than a slab leak repair, and excavation adds to the total when the line runs under the foundation.

  • Continuous meter movement with the main valve closed
  • Warm spots on the floor (a sign of a hot water line leak under a slab)
  • Sewage odor indoors or soggy ground outdoors with no clear irrigation cause
  • Repeated toilet or fixture repairs that don’t stop the leak

Empire Plumbing and Air Conditioning’s licensed technicians (ROC 342717 & 342718) handle exactly this kind of diagnostic work across the Phoenix area, from straightforward supply-line fixes to full slab leak detection.

Your 24 to 48 Hour Action Plan

24 to 48 hour water leak action plan

Here’s how I’d tackle this if it were my own bill. Take a meter reading now and photograph it. Run the toilet dye test tonight. Walk your irrigation system tomorrow morning while the sprinklers are still running. Pull your last two bills and compare billing days side by side.

If none of that turns up an answer within 48 hours, stop guessing and schedule a professional leak detection visit. A hidden leak doesn’t get cheaper by waiting.

— Jason

Get a Professional Leak Check Before the Next Bill Arrives

Empire Plumbing and Air Conditioning gives Phoenix-area homeowners something a DIY meter test can’t: certainty. Once you’ve ruled out the easy fixes, our licensed technicians (ROC 342717 & 342718) bring electronic leak detection equipment that finds the exact location of a hidden or service-line leak, often without tearing up your yard or flooring to look for it.

Empire Plumbing and Air Conditioning

A typical visit starts with a diagnostic assessment, moves to a transparent estimate before any work begins, and covers the repair options available for your situation, whether that’s a simple supply-line fix or a full slab leak repair. We serve Phoenix, Scottsdale, Glendale, Peoria, Anthem, Mesa, Tempe, and Gilbert with 24/7 emergency availability, so a leak found at midnight doesn’t have to wait until Monday. If your meter test came back inconclusive or the bill keeps climbing, book a plumbing service appointment and get a technician on-site before the next billing cycle closes.

Where to Check for Yourself

A few government and utility pages back up nearly everything in this guide, and they’re worth bookmarking if you want to dig deeper on your own.

The EPA WaterSense site breaks down national residential water-use statistics by fixture type, useful context for understanding why toilets and washers dominate most households’ usage. Portland Water Bureau’s leak page walks through its adjustment process in plain language. The City of Davison’s common causes PDF is one of the clearest municipal breakdowns of what typically drives a bill up. Austin Water’s leak page offers the step-by-step meter test referenced throughout this guide. For a quick homeowner checklist with photos, the plumbing tips at AG-Plumbing cover many of the same checks in a shorter format.

Sources

Do not wait for a small AC issue to become a major breakdown. If your air conditioner is blowing warm air, making strange noises, leaking water, or failing to cool your home, Empire Plumbing & Air Conditioning can help.

Call 602-275-8400 today to schedule professional A/C repair in Phoenix.

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