Last updated: October 1, 2026
This page explains how WaterBillCalc turns usage and billing rules into estimates. Each calculator’s own rate period and limitations take priority over this general description.
Inputs and units
The tools use US liquid gallons, cubic feet, CCF or HCF, and in some cases liters. CCF and HCF each represent 100 cubic feet. MCF represents 1,000 cubic feet. These units must not be interchanged without conversion.
We generally use approximately 7.48051948 US gallons per cubic foot and 748.051948 gallons per CCF. Displayed conversions are rounded for readability. A calculator may require a utility’s whole billed units, as explained on its page.
Flat and progressive charges
For a flat rate, the usage charge equals consumption expressed in the rate’s billing unit multiplied by the rate. For example, 5,000 gallons at $6 per 1,000 gallons costs $30.
For progressive tiers, each rate applies only to the portion of consumption inside that tier. The main US calculator supports two tiers. City tools can implement additional tiers when the verified schedule requires them.
Fixed fees, minimums, and billing periods
A fixed fee is added for the period or meter described in the tool. A minimum charge is different: the applicable usage charge is compared with a minimum, and the larger amount is used.
Billing days can change minimums and tier allowances. NYC’s standard metered estimate compares usage charges with its daily water minimum. Boston scales daily tier widths by the entered billing days. Do not multiply a monthly usage total by a quarterly fee without checking the period.
Sewer and other charges
Some tools use the same consumption for water and sewer; the separate water-and-sewer tool lets you enter different billed volumes and rate units. It does not calculate your entitlement to a winter average or allowance.
City rules can use a multiplier, their own tiers, or their own fixed fees. NYC uses the standard wastewater multiplier described on its page. Philadelphia includes the stated TAP-R amounts. Entered other charges are added according to the label and are not independently verified.
Taxes and total formation
A general percentage-tax input applies to the subtotal stated by that calculator. It should be left at zero when the utility uses a different taxable base; a separately calculated amount can be entered as an other charge.
The total is the sum of the calculated charge components. The current city tools round displayed components to cents before adding them so the visible breakdown agrees with the total. Provider rounding may differ.
Special supported cases
Seattle’s tool supports selected inside-city single-family water periods entirely within one rate season. It uses the selected monthly base-charge count and the corresponding peak-tier allowances. It does not automatically estimate the rest of an SPU statement.
Houston’s tool accepts whole billed thousand-gallon units and follows published table amounts, including the conservation-credit boundary. It does not infer how raw meter readings should be rounded into billed units. These limits are shown beside the inputs.
Household usage estimates
The usage tool multiplies shower, toilet, and faucet assumptions by the number of people. Weekly household laundry and dishwasher consumption is divided by seven, then other daily use is added. The daily total is multiplied by the selected number of days.
Starting values are editable examples, not measurements of your home or a certified national average. Actual meter consumption includes activity, outdoor use, and leaks that an estimate may miss.
Validation, tests, and display
Number fields reject missing or negative inputs. Tools that require whole people, billing days, or billed units check those conditions. Extremely large values that produce a non-finite result are rejected.
Checks include known examples, conversion relationships, and material rule boundaries. Examples and reset buttons are checked as part of implementation. Display precision is a presentation choice; it does not imply the source measures consumption to that precision.
Updates and reporting
A rate update requires a source check, formula or data changes where needed, and relevant calculation checks. The source and effective date should be revised together. We do not silently apply a newly discovered rate to an older bill period.
If a result differs from your statement, compare the period, unit, meter class, excluded charges, credits, and rounding. Report reproducible issues to contact@waterbillcalc.com without sending unredacted account information.
Questions about this page? Email contact@waterbillcalc.com.