Sewer charges are based on water use, property size, or a flat fee—whichever method your municipality uses

Your sewer bill is not one thing. Most cities calculate it one of three ways: by measuring the water you use, by the size of your property, or by charging every household the same flat amount. Which method applies to you depends entirely on where you live. Some municipalities use water consumption as a proxy for sewage volume—the logic being that most water entering your home eventually leaves through the sewer. Others charge by lot size or building square footage, assuming larger properties generate more wastewater. A few use a fixed rate regardless of use. Your bill will show which method your local sewer authority has chosen.

The calculation method matters because it determines whether you can lower your bill by using less water, and how predictable your monthly charges will be. Understanding which system your municipality uses takes five minutes and can help you plan your budget or identify ways to reduce costs.

Key Takeaways

  • Water-based sewer charges multiply your water meter reading by a rate per gallon or per thousand gallons, so reducing water use directly lowers your sewer bill.
  • Property-based charges depend on lot size or building area, not on how much water you actually use, and remain the same month to month.
  • Flat-rate systems charge every property the same amount regardless of size or consumption, making your bill predictable but not tied to actual use.
  • Stormwater fees are often added separately and may be based on roof area or impervious surface rather than sewage volume.
  • Your sewer authority's website or a call to their billing department will tell you which calculation method applies to your address.

Water-consumption-based charges: the most common method

If your sewer bill is tied to your water meter, the calculation is straightforward: your water company reads the meter, and the sewer authority charges you a percentage of that usage. The rate is usually expressed as a cost per thousand gallons (often written as per CCF, or hundred cubic feet). For example, if your water meter shows you used 10,000 gallons in a month and your sewer rate is $8 per thousand gallons, your sewer charge would be $80.

This method assumes that roughly 80 to 90 percent of the water entering your home leaves through the sewer system. Water used outdoors—to water a lawn or fill a pool—may not enter the sewer, but most utilities do not separate indoor from outdoor use on a standard meter. Some municipalities offer a separate outdoor meter or allow a deduction if you can document significant outdoor use, but you have to request this and provide proof. The rate itself varies widely by location. A sewer charge of $5 per thousand gallons in one city might be $12 in another, depending on the cost to operate and maintain that city's treatment plants and pipes. Rates also change year to year as infrastructure costs rise.

Property-size-based charges: lot area and building square footage

Some municipalities charge based on the size of your property rather than how much water you use. This method assumes that larger properties—whether residential or commercial—generate more wastewater overall. The charge is usually calculated using either the lot size in square feet or the building footprint, sometimes both.

Under this system, your sewer bill stays the same every month regardless of whether you use a lot of water or very little. A family that showers daily and runs the dishwasher pays the same as a family that uses minimal water, as long as both properties are the same size. This can work in your favor if you are water-conscious, but it means you have no financial incentive to reduce consumption from a sewer perspective. Property-based rates are less common than water-based rates in residential areas but are still used in some regions, particularly in older cities where meter infrastructure is limited or where the sewer system was designed before widespread metering became standard.

Flat-rate systems: the same charge for every property

A flat-rate sewer system charges every household or business the same monthly or annual fee, regardless of property size or water use. This is the simplest method to administer and the easiest for customers to predict, but it does not account for differences in actual wastewater generation.

Flat rates are uncommon in large cities but appear in some smaller municipalities or rural areas where the cost of installing and reading individual meters exceeds the benefit. Under a flat-rate system, your sewer bill is the same whether you live alone in a small cottage or operate a large household with multiple bathrooms. Because there is no connection between your usage and your bill, you have no way to reduce charges through conservation.

Stormwater fees: a separate charge for rainwater runoff

Many municipalities add a stormwater fee to your sewer bill, even though stormwater and sewage are different things. Stormwater is rainwater that runs off your roof, driveway, and yard into storm drains. Sewage is wastewater from toilets, sinks, and appliances. Some cities have separate pipes for each; others combine them into one system.

Stormwater fees are usually calculated based on the amount of impervious surface on your property—that is, surfaces that do not absorb water, such as roofs, driveways, patios, and concrete. The more impervious surface you have, the more stormwater runoff your property generates, and the higher your fee. Some utilities measure this by roof area alone; others include all hard surfaces. A few municipalities allow you to reduce your stormwater fee by installing rain gardens, permeable pavement, or rain barrels that capture runoff instead of letting it run into the storm drain. If your city offers this, you may need to submit photos or have an inspector verify the installation.

How to find out which method your municipality uses

Your sewer bill itself usually states the calculation method in small print, often labeled "Sewer Charge Calculation" or "Rate Schedule." Look for language like "per 1,000 gallons" (water-based), "per square foot" (property-based), or "monthly service charge" (flat rate).

If your bill does not make it clear, call your local sewer authority or water utility directly. Most municipalities have a billing department that can explain your specific rate in minutes. You can also visit the utility's website, where rate schedules are usually posted as PDF documents. Search for "[your city] sewer rates" or "[your city] water and sewer rates" to find the official schedule. If you are moving to a new area or considering a property purchase, ask the current owner or the real estate agent what sewer calculation method is used there. This affects your monthly costs and can vary significantly between neighboring towns.

Why rates change and how to read rate increases

Sewer rates increase regularly because treatment plants, pipes, and pumping stations require maintenance, repair, and replacement. These are expensive, long-lived assets. A rate increase notice will usually explain what the money is being used for—for example, "pipe replacement program" or "treatment plant upgrades." The notice will also show the old rate and the new rate side by side so you can see the dollar amount of the change.

Rate increases are set by the local sewer authority or city council and are public information. If you want to understand or challenge a rate increase, you can attend a public hearing (most cities hold one before a rate change takes effect) or request the rate study document, which breaks down the costs driving the increase. These documents are often available on the municipality's website or by calling the billing department.

Frequently Asked Questions

Does my sewer bill go down if I use less water?

Only if your municipality uses water-consumption-based charges. If you are on a property-size or flat-rate system, your sewer bill will not change based on how much water you use. Check your bill or call your sewer authority to confirm which method applies to you.

Why is my sewer charge higher than my water charge?

Sewer treatment is expensive. It costs money to collect wastewater, transport it through pipes, treat it at a plant, and discharge it safely. In many places, sewer rates are higher than water rates because treatment costs more than delivery. Some utilities also bundle stormwater fees into the sewer line item, which adds to the total.

Can I get a credit if I have a pool or water my lawn a lot?

Some utilities offer a separate outdoor meter or allow a deduction for documented outdoor use, but you have to request it and usually provide proof. Call your water or sewer authority to ask whether this option exists in your area and what documentation they need.

What is an impervious surface, and does it affect my bill?

Impervious surface is any hard material that does not absorb water—roofs, driveways, patios, concrete. If your municipality charges a stormwater fee, it is usually based on how much impervious surface your property has, because that determines how much rainwater runs off into storm drains.

How often do sewer rates change?

Rate changes vary by location. Some municipalities adjust rates annually; others do so every few years. Your sewer authority will send a notice before any rate change takes effect, and the notice will explain the reason and the new amount.