What Is the Sewer Charge on Your Water Bill?

The sewer charge on your water bill is the fee for carrying wastewater away from your home and treating it before it returns to the environment. Because most properties have no meter on the drain line, utilities almost always work it out from the water you use instead: every gallon that comes in, an average of your low-use winter months, or a flat fee. Here is how each method works, why the sewer line can rival the water line, and what you can do about it.

What the sewer charge is

Wastewater is everything that goes down your drains and toilets. Once it leaves your house it travels through a network of collection pipes and pump stations to a treatment plant, where it is cleaned to meet discharge standards. The sewer charge pays for that whole chain: the pipes, the pumping, the plant, the staff, and the debt on upgrades.

A sewer charge usually has two parts:

• A fixed service charge. A flat monthly amount you pay for being connected to the system, whether you use much water or not.
• A volume charge. A rate applied to the amount of wastewater the utility assigns to your account, typically quoted per 1,000 gallons or per CCF.

Treating wastewater is a separate job from supplying drinking water, which is why it shows up as its own line. Some utilities bill both services together under one account; others send two bills.

Why it's based on your water use

Measuring wastewater directly would mean a second meter on every sewer lateral, and that is expensive to install and read. So utilities take a shortcut: they bill sewer from the water meter and assume that most of what came in went down the drain. The U.S. EPA notes that while some utilities measure both the water entering a home and the waste leaving it, many have only one meter and charge both volumes based on the water entering the house.

The assumption holds well for indoor use. Water from your shower, sinks, dishwasher and washing machine all ends up in the sewer. It breaks down outdoors: water that soaks into a lawn, fills a pool or washes a car never reaches the sewer, but a simple meter can't tell the difference. Most of the variety in how sewer is billed is just different answers to that one problem.

Skip the mathSewer Bill Calculator Open →

How utilities calculate it

Five approaches cover nearly every bill you will meet. The most useful question to ask about yours is whether summer watering raises the sewer line.

Utilities that bill a percentage of metered water are trying to be a little fairer, since some indoor water (cooking, drinking, plants) never reaches the drain. Where a flat fee is used, your sewer cost is predictable but gives you no financial reason to cut indoor use.

The sewer charge formula, with an example

Whatever the method, the arithmetic is the same: a fixed charge plus a rate times the billable volume.

Many bills show water in CCF (hundred cubic feet) rather than gallons. One CCF is about 748 gallons, so divide a CCF rate by 0.748 to compare it with a per-1,000-gallon rate.

Here is a worked comparison using made-up round numbers, not any real utility's rates: a $12 fixed charge, a sewer rate of $7.00 per 1,000 gallons, and a household whose winter average is 5,000 gallons a month.

You can plug in your own rates and usage with the sewer bill calculator.

How winter averaging works

Winter averaging uses the months when almost no one waters a lawn as a stand-in for your indoor use. The utility averages your consumption across a set winter window and bills sewer on that figure all year, or bills the lower of the winter average and your actual use in the warm months.

Seattle Public Utilities, for example, bases a single-family household's summer sewer bill on its average winter use when that is lower than its actual summer use, so lawn, garden and car-washing water is not charged as sewer. If you use less in summer than in winter, you are billed on the lower summer figure. The exact months, caps and rules differ by utility.

New customers have no winter history yet, so many utilities assign a default volume, often a citywide average, until one builds up.

Why your sewer charge may be high

If the sewer line looks out of proportion, one of these is usually behind it:

• A leak or running toilet. Water that leaks inside the house goes straight to the drain, so you pay for it as water and again as sewer.
• Outdoor use on a full-metering utility. Irrigation, pool filling and washing vehicles are all counted as wastewater if no averaging or credit applies.
• An inflated winter baseline. See the callout above: an unusual winter can set a higher charge for the whole year.
• Rate increases. Sewer systems are capital-intensive. Utilities raise rates to pay for pipe replacement, plant upgrades and regulatory requirements, so the volume rate can climb even if your use stays flat.
• A high fixed charge. If the fixed portion dominates, cutting water use trims the bill less than you'd expect.

How to lower it

1. Find out which method your utility uses. The rate page or a call to customer service will tell you whether sewer is billed on full metered use, a winter average, a cap or a flat fee. Everything else depends on that answer.
2. Hunt for leaks. Turn off every fixture and check whether your meter's low-flow indicator still moves. A moving dial points to a leak somewhere downstream of the meter, and a toilet flapper is the most common culprit.
3. Cut indoor use. Efficient toilets, showerheads and aerators lower sewer volume directly on utilities that bill by use, and they keep your winter baseline low on those that average.
4. Ask about credits and separate meters. If you irrigate heavily on a full-metering utility, ask whether a separate irrigation meter or sewer credit is available.
5. Be careful in the averaging window. Fix leaks and dripping fixtures before the winter months the utility measures.

Charges that look like sewer but aren't

A few other items often sit next to the sewer line and get mistaken for it:

• Stormwater or drainage fees. These pay for managing rain runoff and are often tied to property size or paved area, not your water use.
• Trash or solid waste. Some municipalities fold it into the same utility bill.
• Connection or tap fees. One-time charges to connect a new building to the system, not part of the monthly bill.

If you are on a septic system, you are not connected to a municipal sewer and pay no sewer charge. The trade-off is that pumping, inspection and repairs are your own responsibility.

The bottom line

The sewer charge pays for carrying away and treating the wastewater your home produces, and because there is rarely a meter on the drain, it is almost always estimated from your water use. Whether that estimate counts every gallon, a winter average or a flat fee decides how much your own habits can move it. Find out which method your utility uses, fix leaks early, and use the calculator below to see what a change in usage does to your bill.