In short: comparing two water bills is usage × rate + fixed charge, done twice. At 5,000 gallons, a plan billing $6.50 per 1,000 gallons with a $15 fixed charge costs $47.50, while a plan billing $8.75 per 1,000 gallons with a $20 fixed charge costs $63.75 — a $16.25 monthly difference ($195 a year), about 34% more. Use the calculator above to compare your own two scenarios.
Rates and charges vary enormously by utility and location — this tool does not look up real tariffs. Enter your own rate sheet figures for an accurate comparison.
How to compare two water bills
Most residential water bills follow the same basic structure — a per-unit usage charge plus a flat monthly service fee:
Worked example. Scenario A: 5,000 gallons at $6.50 per 1,000 gallons plus a $15 fixed charge — (5,000 ÷ 1,000) × 6.50 + 15 = $47.50. Scenario B: the same 5,000 gallons at $8.75 per 1,000 gallons plus a $20 fixed charge — (5,000 ÷ 1,000) × 8.75 + 20 = $63.75. The difference: $16.25 a month, or $195 a year — about 34.2% more for Scenario B.
Same usage, different question. Keep both usage fields equal to compare two rate plans head-to-head. Or keep the rate and fixed charge identical in both scenarios and change only the usage figure to see what a specific reduction — from fixing a leak or switching to low-flow fixtures — would be worth on your actual bill.
Why fixed charges, rate and usage change the answer
Fixed charges dominate at low usage. A flat monthly fee is the same regardless of how much water flows through the meter, so it makes up a bigger share of a light user's bill than a heavy user's. Two plans with a big fixed-charge gap will look most different at low usage and converge as usage climbs.
The usage rate scales with consumption. Every extra 1,000 gallons costs the same additional amount under a flat rate, so the dollar gap between two plans with different per-unit rates grows steadily — even while the percentage difference stays fairly constant, as the table below shows.
Billing units can hide a real difference. A rate of $6.50 per 1,000 gallons and $4.75 per CCF (748 gallons) are not directly comparable numbers on the page — the second one is actually more expensive per gallon. Always compare the calculated total, not the raw rate figures.
Reference: how the difference scales with usage
Using the calculator's default rates (A: $6.50/1,000 gal + $15 fixed; B: $8.75/1,000 gal + $20 fixed), the dollar gap grows with usage while the percentage stays roughly steady.
| Usage | Bill A | Bill B | Difference | % more |
|---|---|---|---|---|
| 2,000 gal | $28.00 | $37.50 | $9.50 | 33.9% |
| 5,000 gal (default) | $47.50 | $63.75 | $16.25 | 34.2% |
| 8,000 gal | $67.00 | $90.00 | $23.00 | 34.3% |
| 12,000 gal | $93.00 | $125.00 | $32.00 | 34.4% |
| 15,000 gal | $112.50 | $151.25 | $38.75 | 34.4% |
Worked examples
5,000 gal, two rate plans
$16.25/mo
The calculator's default: Scenario B costs about 34% more than Scenario A at identical usage — $195 a year.
Light user, 2,000 gal
$9.50/mo
Same two rate plans at lower usage: the dollar gap shrinks, but the percentage difference (33.9%) barely moves.
Heavy user, 12,000 gal
$32.00/mo
The same comparison at high usage: a much bigger dollar gap — $384 a year — for a nearly identical percentage difference.
Frequently asked questions
What can I compare with this calculator?
Anything expressed as usage × rate + fixed charge: two different utility rate plans, your bill before and after a rate increase, two months with different usage, or a proposed conservation project's effect on your bill. Enter each scenario's own usage, rate and fixed charge independently.
Why do fixed charges matter more at low usage?
A fixed monthly service charge is the same no matter how much water you use, so it makes up a larger share of the bill when usage is low and a smaller share as usage grows. Two plans with similar fixed charges but different usage rates will show the biggest percentage difference at low usage, and converge as usage rises.
Does this include sewer charges?
No. Many utilities bill sewer service separately, often based on water usage, sometimes capped at a winter-average baseline. This tool compares water charges only — see the sewer bill calculator to estimate that portion separately and add it to each scenario.
Does this handle tiered (block) rate structures?
No, this tool uses a single flat rate per scenario. If either plan charges a different rate for different usage tiers (for example, a higher rate above 10,000 gallons), use the water rate tier calculator to work out that scenario's true bill first, then bring the total into this comparison.
Why might my two rate plans use different billing units?
Utilities aren't consistent about this: some bill per 1,000 gallons, others per CCF (748 gallons), and some in cubic meters. This calculator lets each scenario use its own billing unit so you can compare real rate sheets exactly as published, without converting them yourself first.
Can I use this to estimate savings from using less water?
Yes — enter the same rate and fixed charge in both scenarios, then set a lower usage figure in one of them to see the monthly and annual dollar difference from that reduction alone, with no rate change involved.
Sources & references
- American Water Works Association (AWWA). Manual M1: Principles of Water Rates, Fees, and Charges.
John Mac, PE
Water Systems Specialist · Austin, Texas
Texas-licensed Professional Engineer with 13+ years in residential water systems and 180+ completed projects. Writes and reviews the calculators on watercalculator.us. Read full bio
Texas PE (2016) · BS Civil Engineering, Hydraulics (2013)