In short: a sewer bill is usually a fixed service charge plus a usage charge — your metered water use multiplied by a flat or tiered sewer rate. Many utilities also cap the billed usage at your winter-average water use, since outdoor watering doesn't go down the drain. Enter your own numbers above for a bill tailored to your utility.
This is a planning estimate built from the numbers you enter. Your actual bill depends on your utility's specific rate schedule, taxes and fees — use it to fine-tune the inputs here.
How the sewer bill is calculated
Most residential sewer bills have two parts: a fixed charge that covers the sewer system regardless of use, and a usage charge based on metered water. Very few utilities meter what actually goes down the drain, so they bill sewer service using the water meter as a stand-in:
sewer bill = fixed charge + (billed usage × sewer rate)
Billed usage is your metered water use, or your winter-average cap if it's lower and your utility applies one. The sewer rate can be a single flat rate, or a tiered rate that charges more per unit as usage rises.
Worked example. A household used 6 CCF (4,488 gallons) of water this billing period, on a flat rate of $4.85 per CCF with an $18.50 fixed charge. The usage charge is 6 × $4.85 = $29.10, so the total sewer bill is $18.50 + $29.10 = $47.60 for the period, or about $10.61 per 1,000 gallons.
How tiered (block) rates work
A tiered rate splits usage into blocks and charges a different rate for each one — usually cheaper for the first block and pricier above it, to encourage conservation. Each tier's rate only applies to the usage that falls inside that tier, not the whole bill.
Worked example. Suppose a utility instead billed in two tiers — Tier 1: up to 4 CCF at $3.50, Tier 2: above 4 CCF at $5.25 — with the same $18.50 fixed charge. For the same 6 CCF of use: the first 4 CCF costs 4 × $3.50 = $14.00, and the remaining 2 CCF costs 2 × $5.25 = $10.50, for a $24.50 usage charge and a $43.00 total bill. Switch the calculator above to "Tiered rate" to try your own tiers.
Why sewer bills use a winter average
Outdoor watering — lawns, gardens, pools, car washing — soaks into the ground or evaporates rather than flowing to the treatment plant, so it shouldn't count as sewer usage. Because most homes don't have a second meter to separate indoor and outdoor water, many utilities instead look at your metered use during winter months, when outdoor watering is minimal, and use that as a cap on billed sewer usage year-round.
Worked example. A household's winter-average use is 4 CCF, but a summer reading comes in at 9 CCF because of lawn irrigation. Billed on the actual 9 CCF at $4.85 per CCF, the usage charge would be $43.65 and the total bill $62.15. Capped at the 4 CCF winter average instead, the usage charge is $19.40 and the total bill is $37.90 — a $24.25 saving for that period. Check the box above to see this applied to your own numbers.
Common billing units
Utilities bill water and sewer in different units. Use whichever one matches your bill or rate schedule — the calculator converts between them automatically.
| Unit | Also called | Equal to |
|---|---|---|
| CCF | Hundred cubic feet | 748 gallons |
| 1,000 gal | Kgal, MG/1000 | 1,000 gallons |
| Gallon | Gal | 1 gallon |
| Cubic meter | m³, kL | 264.172 gallons |
1 CCF = 100 cubic feet = 748.05 gallons, commonly rounded to 748. 1 cubic meter = 1,000 liters = 264.172 US gallons.
How to bring the number down
Fix leaks first. A running toilet or dripping faucet adds directly to your metered indoor use — and therefore to your sewer bill — every single day it runs. Check for a leak with the running toilet cost calculator or the water leak cost calculator.
Focus on indoor use. Because sewer usage is usually capped at a winter average, cutting outdoor watering rarely lowers the sewer portion of your bill. Shorter showers, full laundry and dishwasher loads, and efficient fixtures reduce the indoor use that sewer rates actually charge for.
Read your rate schedule. Compare the fixed charge, the rate structure (flat or tiered) and whether a winter-average cap applies — these vary widely by utility and change the shape of the bill more than any single habit. The water rate tier calculator can help you check a tiered water rate the same way.
Frequently asked questions
What is a sewer bill based on?
Most sewer bills combine a fixed monthly service charge with a usage charge equal to your metered water use multiplied by a sewer rate. The rate can be a single flat rate per unit or a tiered (block) rate that charges more per unit as usage rises. Very few utilities meter wastewater directly, so water use stands in for sewer use.
Why does my sewer bill use a winter-average cap instead of my actual water use?
Sewer charges are meant to reflect wastewater sent to the treatment plant, but outdoor water use like irrigation soaks into the ground instead of going down the drain. Many utilities cap billed sewer usage at a customer's average metered use during winter months, when outdoor watering is minimal, so summer irrigation isn't billed as sewer use.
Do sewer rates use tiered pricing like water rates?
Some do. A tiered or block rate charges a lower price for the first block of usage and a higher price for usage above that threshold, similar to how many water rates are structured. Other utilities use a single flat rate for all sewer usage. Check your utility's published rate schedule to see which applies to you.
Can my sewer bill be higher than my water bill?
Yes. Treating and processing wastewater is often more expensive than treating and delivering clean water, so sewer rates and fixed charges can exceed water rates for the same utility. Some combined water-and-sewer bills show the sewer portion as the larger line item.
How can I lower my sewer bill?
Since sewer charges are usually based on indoor water use, fixing leaks and cutting indoor use in showers, toilets, faucets and appliances lowers the bill directly. Outdoor irrigation usually has little effect if your utility applies a winter-average cap, since that water is already excluded from the sewer usage charge.
Sources & references
- American Water Works Association (AWWA) & Water Environment Federation (WEF). Manual of Practice on utility rate-setting principles.
- U.S. Environmental Protection Agency (EPA), Office of Wastewater Management. Guidance on setting user charges for wastewater systems.
- U.S. Geological Survey (USGS). Water Q&A: Water use at home.
There is no single national sewer rate — fixed charges, rate structures and winter-average rules vary by utility. Always check your own bill or your utility's published rate schedule rather than relying on the defaults above.
Sarah Bennett, MS
Water Quality & Sustainability Specialist · Portland, Oregon
Environmental scientist (MS, Water Resources) with 9+ years in residential water quality, treatment, and usage efficiency, and 150+ completed assessments. Sarah writes and reviews the treatment, usage, and cost calculators on watercalculator.us. Read full bio
MS Environmental Science, Water Resources (2018) · BS Environmental Engineering (2016)