A water bill that jumps for no obvious reason is one of the most reliable signs of a leak somewhere in your home. Before you assume your utility raised rates, it's worth spending 20 minutes ruling out the usual suspects, because the fix is often cheap and the water waste adds up fast if you wait.
Could It Just Be a Leak?
Statistically, yes. The average household leak wastes about 9,400 gallons of water a year — roughly what it takes to wash 300 loads of laundry — and about 10% of homes have leaks that waste 90 gallons or more per day, according to the EPA's WaterSense program. That's the kind of volume that shows up clearly on a bill, even before you can see or hear anything wrong.
The fastest way to confirm a leak exists is to check your water meter. Turn off every faucet, appliance, and irrigation zone in the house, then find your meter (usually near the curb or in a utility box) and watch the leak indicator, a small triangle or dial that spins if water is still moving. If it's turning with everything off, water is escaping somewhere between the meter and your fixtures.
Is It Your Toilet?
Toilets are the single most common source of a mystery spike. A worn flapper or fill valve can let water silently trickle from the tank into the bowl, and a bad one can waste up to 200 gallons a day without ever making a sound you'd notice. To test it, add a few drops of food coloring or a dye tablet to the tank and wait 10 minutes without flushing. If color shows up in the bowl, the tank is leaking into it.
The fix is usually inexpensive. A replacement flapper runs about $5 to $15 as a DIY part, and a full parts kit (flapper, fill valve, flush valve) typically costs $20 to $35. If you'd rather hire it out, professional toilet repair averages $100 to $400, according to Angi's 2026 cost data. Check every toilet in the house — it's common for only one to be the culprit.
Could It Be a Slab Leak?
If your home sits on a concrete slab and you've ruled out toilets and visible fixtures, a slab leak — a break in a water line running under the foundation — is worth considering. Warning signs include warm spots on the floor (usually a hot water line), the sound of running water when everything's off, unexplained cracks in flooring or walls, and, of course, a water bill that keeps climbing.
Slab leaks are harder to fix than a toilet, and pricing depends heavily on how the pipe is accessed. Repairs average around $2,280 including leak detection, but can range from $300 for a minor, accessible leak up to $6,750 for one that's difficult to reach, per Angi's slab leak repair data. If a slab leak is suspected, this is a job for a licensed plumber with leak-detection equipment, not a DIY project.
What About Irrigation and Outdoor Leaks?
Sprinkler systems and outdoor spigots are another common source, especially if a line was nicked during yard work or a valve is stuck open. Look for soggy patches in the lawn, unusually green or lush spots, or water pooling near a valve box. Irrigation repairs typically run $100 to $400 on average, with minor fixes like a cracked head starting around $50 and major underground pipe repairs reaching $600 or more, according to HomeGuide's irrigation repair cost guide.
If your water heater is aging, it's also worth checking connections and the drain valve for slow seepage — a failing unit can waste water for weeks before it fails outright. If yours is due, see How Much Does It Cost to Replace a Water Heater in 2026? for what a replacement typically runs.
Common Leak Sources at a Glance
| Leak Source | Typical Water Waste | Typical Repair Cost |
|---|---|---|
| Running toilet | Up to 200 gallons/day | $5–$35 (DIY) / $100–$400 (pro) |
| Dripping faucet | About 3,000 gallons/year | Usually a low-cost part swap |
| Irrigation/sprinkler line | Varies with leak size | $100–$400 typical; $600+ for major repairs |
| Slab leak | Varies, often significant | $2,280 average; $300–$6,750 range |
When Should You Call a Plumber?
If the meter test confirms a leak but you can't find it after checking toilets, faucets, and visible irrigation lines, it's time to call in a pro. Slab leaks and anything involving the main line under the house require specialized detection equipment most homeowners don't have. It also helps to get more than one quote before authorizing repair work — plumbing rates vary by market and by the complexity of the job, and knowing what a fair price actually looks like beats hoping the first number you hear is reasonable. For a sense of typical rates, see How Much Does a Plumber Cost Per Hour in 2026?.
What to Do About It
Work through this in order:
- Check the meter. Shut off all water use and watch the leak indicator for movement.
- Test every toilet. Use dye or food coloring and wait 10 minutes without flushing.
- Inspect visible fixtures. Check under sinks, around the water heater, and at outdoor spigots for damp spots.
- Walk the yard. Look for soggy patches, pooling near valve boxes, or unusually lush grass along irrigation lines.
- Rule out a slab leak. Feel for warm spots on the floor and listen for running water with everything off.
- Call a licensed plumber if the meter still shows movement after steps 1–5, and get more than one quote before committing to a repair.
A higher water bill is annoying, but it's usually a solvable problem once you know where to look.