Your sewer bill is high because of how it's calculated, not always because you're using more water

A sewer bill spike usually comes from one of three places: a leak in your home's plumbing, a change in how your municipality charges, or actual increased water use. The tricky part is that your sewer charge is almost always based on your water meter reading, so even if nothing is wrong with your sewer line itself, a higher water bill automatically means a higher sewer bill. Before you call a plumber, check whether your water use actually went up, whether your rate changed, or whether you have a hidden leak.

Most municipalities charge sewer fees as a percentage of water consumption—typically 80 to 100 percent of what your water meter shows. Some charge a flat fee per household regardless of use, and a few use a combination. If your water bill stayed the same but your sewer bill rose, ask your utility company whether they changed their rate structure or whether you're now in a different billing tier. If both bills rose together, you almost certainly used more water, and the question becomes why.

Key Takeaways

  • Sewer charges are usually calculated from your water meter, so a higher sewer bill often means you used more water, not that your sewer line is damaged.
  • A silent leak—in a toilet, under a sink, or underground—can add hundreds of gallons a day to your water use without you noticing.
  • Check your water meter before and after a two-hour period when no one is using water; if it moves, you have a leak.
  • Rate increases, seasonal billing changes, and new billing tiers can raise your sewer bill even if your actual use stayed the same.
  • If you find a leak, repair it when ready; a running toilet alone can cost $30 to $50 extra per month in sewer charges.

Check for a hidden leak in your home first

A leak is the most common reason for a sudden jump in your sewer bill, and the most fixable one. The leak is usually in a toilet, under a sink, or in an underground supply line—places you don't see every day. A running toilet can waste 200 gallons a day. A slow drip under a bathroom sink might waste 30 gallons a day. An underground leak in your main water line can waste even more.

To check for a leak, turn off all water in your home—no showers, no laundry, no toilet flushing. Wait two hours. Then look at your water meter (usually in a basement, crawl space, or outside near the street). Write down the number. Wait another two hours with no water use. Check the meter again. If the number changed, you have a leak. If it didn't, your high bill is from actual use or a rate change, not a leak.

If you find a leak, locate it next. Check under sinks and around the toilet base for wet spots or water stains. Listen for running water when nothing is on. If you hear water but see no leak, the problem is likely underground in your main supply line, and you'll need a plumber to locate and repair it. If you see a leak—a dripping faucet, a sweating pipe, water pooling—you may be able to fix it yourself (a running toilet usually just needs a new flapper, about $15), or you can call a plumber.

Review your water meter and billing history

Before assuming you have a leak, pull up your last 12 months of water and sewer bills. Most utilities let you see this online through your account portal, or you can call and ask for a printout. Look for the pattern: did your bill creep up gradually over months, or did it jump suddenly in one billing cycle?

A gradual increase over a season often means seasonal use—more showers in summer, more outdoor watering, more laundry. A sudden jump in one month suggests either a leak that started recently or a meter misread. If your meter reading looks wrong (a jump from 5,000 to 50,000 gallons in one month when you normally use 3,000), call your utility company and ask them to verify the reading. Meter errors do happen, and they can usually correct them if you report them quickly.

Also check whether your utility company changed its rate or billing structure. Some municipalities raise sewer rates annually. Others moved from a flat fee to a tiered system where you pay more per gallon once you exceed a certain threshold. Your bill notice should show the rate, but if it's unclear, call the utility and ask what your current rate is and whether it changed since last year.

Understand how your municipality calculates sewer charges

Sewer bills vary wildly depending on where you live. Some cities charge a flat monthly fee—$30 to $80 per month regardless of how much water you use. Others charge a percentage of your water bill, usually 80 to 100 percent. A few use a tiered system where the rate per gallon increases once you exceed a baseline amount.

If you're on a tiered system and your water use crossed into a higher tier, your sewer bill will jump even if your water use only increased slightly. For example, if your baseline is 3,000 gallons per month at $3 per 100 gallons, and the next tier is $4 per 100 gallons, jumping from 2,900 to 3,100 gallons means your sewer charge goes up by more than the water increase alone would suggest.

Call your utility company's billing department and ask them to explain your rate structure in writing. Ask specifically: Do you charge a flat fee, a percentage of water use, or a tiered rate? If tiered, what are the thresholds? Did the rate change in the last 12 months? A five-minute call can answer whether your bill is high because of how you're charged, not because of what you're using.

Look for seasonal or temporary spikes in your own use

Sometimes the answer is straightforward: you used more water. Summer months often bring higher bills because of lawn watering, more frequent showers, and filling pools or hot tubs. If your bill spiked in June or July and you water your lawn, that's likely why. If it spiked in January and you live somewhere cold, you may have had guests, done extra laundry, or run a humidifier.

Check whether anything changed in your household in the month before the bill jumped. Did you have guests staying over? Did you start a garden or fill a pool? Did a washing machine or dishwasher break and run constantly? Did someone in the house develop a habit of long showers or frequent baths? These things add up quickly. A single load of laundry uses 40 to 50 gallons. A 20-minute shower uses 50 gallons. Watering a lawn for an hour uses 600 gallons or more.

If you can't think of a reason for the spike and it's not summer, and your meter check showed no leak, ask your utility company whether they estimated your last reading instead of actually reading your meter. Some utilities estimate readings if they can't access the meter, and estimates can be wrong. Asking them to do an actual reading can sometimes lower your next bill.

When to call a plumber versus your utility company

Call your utility company first if your bill jumped suddenly with no explanation. They can tell you whether your rate changed, whether they estimated your reading, and what your actual consumption was. This call takes 10 minutes and costs nothing. If they confirm your consumption was high and you found no leak, the high use is real and you need to find where it's going.

Call a plumber if your meter check showed a leak, or if your utility company confirmed high water use and you can't find the source. A plumber can locate underground leaks using sound equipment and can check your fixtures for slow leaks you might miss. Expect to pay $100 to $200 for a leak detection visit. If they find a leak, repair costs depend on what it is—a new toilet flapper is $15 to $50, a faucet repair is $75 to $200, and an underground main line repair can be $500 to $2,500 depending on depth and location.

Do not ignore a leak once you find it. A leak that wastes just 10 gallons a day adds $3 to $5 to your monthly sewer bill, or $36 to $60 a year. A leak that wastes 100 gallons a day adds $30 to $50 a month. The repair usually pays for itself in a few months.

Request an adjustment if the bill was clearly wrong

If your utility company confirms that your meter was misread, that they estimated when they should have read it, or that they applied the wrong rate, ask for a bill adjustment. Most utilities will correct a clear error and credit your account. Some will spread the adjustment over several months so your next bill isn't too low. Get the adjustment in writing so you have a record.

If your bill is high because you actually used more water and you've fixed the leak or stopped the temporary use, your next bill should be lower. If it stays high, call again and ask them to check whether the meter is working correctly. A broken meter can stick at a high reading or advance faster than it should, and utilities can replace them if they're faulty.

Frequently Asked Questions

Can a sewer line problem cause my bill to go up?

Not directly. A broken sewer line doesn't affect your water meter or your bill—it affects what happens to the water after it leaves your house. A leak in your water supply line (the line bringing water into your home) will show up on your meter and raise your bill. A leak in your sewer line (the line taking water away) won't show on your meter and won't raise your bill, but it will cause wet spots in your yard or sewage smells.

Why does my sewer bill say I used 10,000 gallons when I live alone?

That's about 330 gallons per day, which is high for one person but not impossible if you have a leak. Check your meter as described above. If the meter is accurate, look for a running toilet (the most common culprit), a dripping faucet, or a leak under the sink. If you find nothing, call a plumber to check for an underground leak.

My water bill went up but my sewer bill didn't. Is that normal?

Yes. Some water goes to outdoor use—watering a lawn, washing a car, filling a pool—and doesn't enter the sewer system. If you watered your lawn more this month, your water bill rises but your sewer bill may not. If your water bill rose but sewer didn't, you probably used more water outside.

How much does it cost to fix a running toilet?

A running toilet usually needs a new flapper or fill valve, which costs $15 to $50 in parts and takes 15 minutes to replace if you do it yourself. If you call a plumber, expect $75 to $150 total. The repair pays for itself in one to three months because a running toilet can add $30 to $50 to your monthly sewer bill.

Can I dispute my sewer bill if I think it's wrong?

Yes. Contact your utility company's billing department and explain why you think the bill is wrong. Bring your meter readings, your billing history, and any evidence of a leak or rate error. Most utilities have a dispute process and will investigate. If they find an error, they'll adjust your bill. If they don't find an error, you can ask for a payment plan if the bill is large.