Sewer charges are usually based on how much water you use, not on how much sewage you actually produce

Most cities calculate your sewer bill by measuring the water that enters your home through your meter, then charging you a percentage of that amount as a sewer fee. The logic is straightforward: the more water you use, the more wastewater your home generates, so the more it costs the city to treat. A few cities use a flat fee instead, charging every household the same amount regardless of usage. Some charge based on the size of your water meter or the number of people in your household. The method your city uses depends on local policy and infrastructure.

Your sewer bill typically appears on the same statement as your water bill, or sometimes as a separate line item. The charge is usually expressed as a percentage of your water bill—commonly between 50 and 150 percent of what you paid for water, though this varies widely by location. A household using 5,000 gallons of water per month in one city might pay $25 in sewer charges, while the same usage in another city could cost $60.

Key Takeaways

  • Sewer charges are calculated based on water meter readings in most cities, with the assumption that water entering your home becomes wastewater leaving it.
  • The sewer rate is usually a fixed percentage of your water bill, but this percentage differs by city and can range from 50 to 150 percent or higher.
  • Some cities use flat fees, meter size, or household occupancy instead of water usage to determine sewer costs.
  • Outdoor water use (irrigation, filling pools) typically counts toward your sewer charge even though it does not enter the sewer system.

Water meter readings and the sewer calculation

Your water meter is the starting point for almost every sewer bill. A meter reader visits your property monthly or quarterly and records how many gallons passed through the meter. That number becomes the basis for both your water charge and your sewer charge. If your meter shows 6,000 gallons used in a month, the city assumes roughly 6,000 gallons of wastewater entered the sewer system.

The city then applies its sewer rate to that volume. If your city's rate is 80 percent of the water charge, and your water bill was $40, your sewer charge would be $32. Some cities break the rate into tiers—you might pay one rate for the first 3,000 gallons and a higher rate for anything above that—but the meter reading is still the foundation. A few cities meter wastewater separately, installing a second meter on the sewer line leaving your property, but this is uncommon because it is expensive to install and maintain.

Why outdoor water use counts toward your sewer bill

Water you use to water your lawn, wash your car, or fill a swimming pool goes through your meter and counts toward your sewer charge, even though none of it enters the sewer system. This is a common source of confusion on bills. The city charges you for the water itself, and then charges you again for sewer treatment, because the meter cannot distinguish between water that goes down the drain and water that soaks into the ground or evaporates.

Some cities offer a separate outdoor meter or a credit system to address this. If you install a second meter on an outdoor faucet or irrigation line, the water that meter records does not count toward your sewer charge—only the water that actually enters your home does. To set this up, contact your water utility directly. The cost of installing a second meter (typically $100 to $300) may take years to recover through lower sewer charges, so it makes sense only if you use significant amounts of outdoor water.

Flat fees and alternative calculation methods

Not every city uses water volume to calculate sewer charges. Some charge a flat monthly or annual fee to every property, regardless of how much water the household uses. This method is simpler to administer but can feel unfair to households that use less water than average. A family of two might pay the same sewer fee as a family of six.

Other cities base sewer charges on the diameter of your water meter (a proxy for household size and usage potential) or on the number of people living in the home. A few charge based on the square footage of your property or the size of your lot. These alternatives exist because some cities believe water usage is not a fair measure of sewer burden—for example, a business that uses large amounts of water for cooling but produces little wastewater might be overcharged under a usage-based system. To find out which method your city uses, check your bill or call your local water utility.

Stormwater charges and combined sewer systems

Some cities add a separate stormwater fee to your bill, distinct from the sewer charge. Stormwater is rainwater that runs off your roof, driveway, and yard into storm drains. In cities with separate storm and sanitary sewer systems, stormwater does not mix with wastewater and goes directly to a river or treatment pond. In cities with combined systems, stormwater and wastewater share the same pipes, and the city charges you for treating both.

Stormwater fees are often based on the amount of impervious surface on your property—the area of roof, pavement, and other hard surfaces that prevent water from soaking into the ground. A property with a large roof and a long driveway generates more stormwater runoff than a property with mostly grass, so it may pay a higher stormwater fee. Some cities charge a flat stormwater fee to all residential properties. Check your bill to see whether stormwater is listed separately or bundled into your sewer charge.

How cities set sewer rates and when they change

Your city's sewer department calculates rates based on the cost to operate and maintain the sewer system. This includes the salaries of workers, the cost of chemicals used in treatment, repairs to pipes and pumps, and debt service on bonds issued to build or upgrade infrastructure. The department estimates total costs for the coming year, divides by the expected volume of water to be treated, and sets a rate per gallon or per 1,000 gallons. If costs rise or usage drops, rates go up.

Most cities review and adjust sewer rates annually, though the change may be small—2 to 5 percent in many places. Larger increases happen when a city undertakes a major infrastructure project, such as replacing aging pipes or upgrading a treatment plant. These projects can trigger rate increases of 10 to 20 percent or more over several years. Your city should notify you before a rate change takes effect, usually through a notice in the mail or a public hearing announcement.

Reading your sewer charge on your bill

Your sewer charge appears as a line item on your water bill, usually labeled "Sewer," "Wastewater," or "Sanitary Sewer." Next to it you will see a volume (in gallons or hundred-cubic-feet) and a rate (dollars per unit). Multiply the volume by the rate to verify the charge. If your bill shows 5,000 gallons and a rate of $0.006 per gallon, your sewer charge should be $30.

Some bills also show a base or fixed charge, which is a flat fee added to the usage-based charge. This covers the cost of maintaining the connection to your home, regardless of how much water you use. If your bill shows a base charge of $10 and a usage charge of $30, your total sewer bill is $40. Check your bill for any additional line items, such as stormwater or treatment plant fees, which may be listed separately or combined into a single sewer total.

Frequently Asked Questions

Why do I pay sewer charges for water I use outside?

Your water meter cannot tell the difference between water that goes down a drain and water that waters your lawn. The city charges based on total water volume entering your property. If you use significant outdoor water, ask your utility about installing a separate outdoor meter, which would exclude that water from your sewer charge.

Can I reduce my sewer bill by using less water?

Yes, if your city uses usage-based rates. Shorter showers, fixing leaks, and running full loads in your dishwasher and washing machine all lower your water meter reading, which directly reduces both your water and sewer charges. If your city charges a flat sewer fee, reducing water use will lower your water bill but not your sewer bill.

What is the difference between sewer and stormwater charges?

Sewer charges cover the cost of treating wastewater from your home (toilets, sinks, showers). Stormwater charges cover the cost of managing rainwater runoff from your property. Not all cities charge for stormwater separately; some include it in the sewer bill or do not charge for it at all.

Why did my sewer bill increase so much?

The most common reasons are a rate increase set by your city, higher water usage during the billing period, or a change in how the city calculates charges. Check whether your water meter reading increased compared to the previous month. If usage is the same but the rate changed, your city likely raised sewer rates; you should have received a notice in the mail.

How do I know if my sewer bill is correct?

Verify the water meter reading on your bill, then multiply it by the sewer rate shown on the bill. The result should match your sewer charge. If the math does not add up, contact your water utility. Also check that the meter reading is reasonable compared to previous months—a sudden spike might indicate a leak in your home.