To estimate a water and sewer bill, subtract the previous meter reading from the current one, convert the difference to the units your utility bills, then apply that utility’s current water and sewer rates. Add fixed charges and other fees. The result is an estimate—not necessarily the bill total—because utilities can use different rounding rules, tiered rates, sewer-volume rules, and billing periods.
What you need for a useful estimate
- The previous and current readings from the same meter, plus the dates they were taken.
- The meter’s units and the utility’s method for handling decimal or fractional digits.
- The applicable rate schedule for your service address, account class, meter size, and billing period.
- The utility’s rules for sewer volume and any fixed, stormwater, drainage, or other charges.
Without the address-specific utility, readings, and applicable rate schedule, it is not possible to calculate a meaningful dollar amount. Use your utility’s current official rate page, account portal, or calculator rather than borrowing a rate from another city.
Calculate water use from the meter readings
- Confirm the readings. Use the start and end readings for the same meter. Note the reading dates; if you are estimating between bills, record both readings yourself and count the days between them. DC Water likewise advises customers to record the start and end readings and subtract the first from the latter (DC Water meter guidance).
- Subtract the earlier reading.
Current reading − previous reading = usage for the period. Check the bill or meter documentation to determine whether to include fractional digits and how the utility rounds usage. DC Water bills in whole ccf and its example disregards fractional digits; other utilities can handle units and fractions differently. - Convert the usage if needed. Match your result to the unit used in the rate schedule. One ccf (100 cubic feet) equals 748 gallons, according to the City of Portland’s water rate page. Do not assume that your utility bills in ccf or uses the same rounding convention.
Apply your utility’s water rates
Find the rate schedule that covers your service address and the dates in the billing period. Check its effective dates, account class, and meter size. A flat volumetric rate is calculated by multiplying billable usage by the rate. With tiered rates, divide usage among the rate blocks and charge each block at its own price. If the tariff sets tiers by daily use, use the number of service days—not an assumed monthly period—to find the applicable tier amounts.
For example, WSSC Water’s published illustration uses 13,000 gallons over 90 days, or about 144 gallons per day. In that example, 7,290 gallons are in tier 1 and the remaining 5,710 gallons are in tier 2; the page shows a $100.72 water charge using the rates in its example table. These figures illustrate WSSC’s calculation, not a general rate or a substitute for checking current rates for an account (WSSC Water bill explanation).
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- Short press the button to change the mode: Flow Mode: real-time water flow rate; Consumption Mode: last-time water usage; Average Mode: daily average water usage of a week (count from next day); Total Mode: total water usage.
- Long press the button at flow mode to switch the unit (US gallon to liter). Reset data when long press the button at other modes. The LCD screen goes to sleep automatically if there is no operation in 1 minute.
- Built-in with hall type sensor and IC chipset, which provide more accurate measurement and precise calculations. Ideal to measure how much amount of water are used and prevent over-watering.
Estimate the sewer charge separately
Many residences do not have a separate sewer meter, so utilities may base sewer volume on water use. The sewer calculation may nevertheless use a different volume from the current water reading. Check the local rule for your account; a winter average, class average, cap, or sewer submeter can change the billable sewer volume.
- Portland: Residential sewer volume can be based on a winter average or class average, as described in its water and sewer rate information.
- Henrico County: Its described single-family rule uses the lower of actual use or first-cycle use. Its published 2026/2027 example is specific to Henrico County and that rate period (Henrico County water and sewer rates).
- WSSC Water: Its guidance says sewer charges use water consumption unless there is a submeter (WSSC Water bill explanation).
Once you have the billable sewer volume under your utility’s rule, apply the current sewer rate and any sewer-specific fixed charge. Do not automatically multiply the water reading by the sewer rate unless the utility’s rules say that is the correct basis.
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Add fixed charges and other fees
Usage charges may be only part of the total. Check the rate schedule and bill for service or meter-size charges and applicable stormwater, drainage, replacement, infrastructure, state, or other fees. DC Water lists meter, water service replacement, impervious-area, and District fees among charges customers may need to add to estimate the full bill (DC Water meter guidance).
Online calculators also have limits. Houston Water’s calculator applies to single-family residential accounts with a 5/8-inch meter, uses rates effective April 1, 2026 through March 31, 2027, and excludes drainage fees. Check that a calculator covers your account and see which charges it leaves out before relying on its total (Houston Water bill estimator).
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- Equipped with an easy-to-read LCD screen and one-touch control push button, this water flow meter can easily display and track the water usage & flow rate of your outdoor garden hose with 4 different measurement modes.
- Short press the button to change the mode from FLOW / CONSUMPTION / AVERAGE / TOTAL. Flow Mode: real-time water flow rate | Consumption Mode: last-time water usage | Average Mode: daily average water usage of a week (count from next day) | Total Mode: total water usage.
- Long press the button at flow mode to switch the unit (gallon to liter). Reset data when long press the button at other modes. The LCD screen goes to sleep automatically if there is no operation/water flow in 1 minute.
- Built-in with hall type sensor and IC chipset, which provide more accurate measurement and precise calculations. The measurement tolerance is less than 5%, great to measure how much amount of water are used and prevent over-watering.
Work through a utility’s example without treating it as your rate
Henrico County’s published 2026/2027 two-month example shows how separate water and sewer charges, service charges, and volume rates combine:
| Charge | Calculation in Henrico’s example | Example amount |
|---|---|---|
| Water | 20 ccf × $4.82, plus a $20.95 water service charge | $117.35 |
| Sewer | 20 ccf × $5.10, plus a $42.30 sewer service charge | $144.30 |
| Total | Water plus sewer | $261.65 |
Those rates and charges apply to Henrico County’s stated example and rate period, not to households generally. Use the example to understand the arithmetic; use the schedule serving your own address for an estimate.
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Reconcile your estimate with the bill
If your calculation differs from the bill, compare the inputs and rules one by one:
- Are the readings for the same meter, and do their dates match the bill period?
- Did you subtract the earlier reading from the later one and use the right units?
- Does the utility bill whole units, disregard fractions, or round differently?
- Did you use the current rate schedule for the account class, meter size, and service dates?
- Did you apply tier thresholds using the correct number of service days?
- Is sewer volume based on current use, an average, a cap, or a separate submeter?
- Did you include fixed charges and applicable fees, and exclude any items the calculator omits?
For tiered tariffs, a small change in usage or service days can move some consumption into another rate block. If a material difference remains, check the utility’s bill explanation and account-specific rules.
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