Your water bill doubled. Here’s which part actually changed.
Type your normal bill (A) and your high bill (B). The bars split the difference into the parts that moved.
70% of your $60.00 increase is more water used per day.
Usage: 150 → 272 gallons a day (+82%). Effective usage price: $10.03 → $11.70 per 1,000 gallons.
Usage per day went up 82%. Rule out a leak first: EPA says to read your meter before and after a two-hour period with no water use; if it moves at all, you probably have a leak (EPA WaterSense (accessed October 4, 2026)).
No leak? Look outside next: irrigation timer spikes and outdoor watering.
Estimate: at bill B’s usage per day, a 30-day bill would be about $115.45. Assumes usage charges scale with days at bill B’s average price and fixed charges and fees stay the same. Tiers can push a longer bill higher.
Show the math
Usage is converted to gallons (g). D is billing days, u = g ÷ D is gallons a day, r = usage $ ÷ g is the average price. A bar over a letter means the average of bill A and bill B; Δ means B − A.
Bill A: g = 4,488 gal, D = 30, u = 149.6 gal/day, r = $10.03 per 1,000 gal Bill B: g = 8,977 gal, D = 33, u = 272.0 gal/day, r = $11.70 per 1,000 gal Billing days = r̄ × ū × ΔD = +$6.87 Usage per day = r̄ × D̄ × Δu = +$41.88 Rate or tier = ḡ × Δr = +$11.25 Water usage change = +$60.00 Sewer uses the same split: days $0.00 + usage/day $0.00 + rate $0.00 = $0.00 Fixed, other fees and adjustments: B − A, as typed. All bars together = +$60.00
Why it adds up exactly: ū·ΔD + D̄·Δu equals Δg, and r̄·Δg + ḡ·Δr equals the change in r·g, which is the change in the usage charge. Using averages on both sides (the midpoint, or symmetric, split) leaves no unexplained “interaction” remainder, and it gives the same answer if you swap which bill is A. Each bar is rounded to the cent so the bars still sum to the rounded total.
Units: one CCF (also called HCF, 100 cubic feet) is 748 gallons per EPA WaterSense (accessed October 4, 2026); the tool uses 748.052. One cubic foot is 7.48052 gallons and one cubic meter is 264.172 gallons, computed from NIST’s factors (1 ft³ = 0.02831685 m³, 1 US gal = 0.003785412 m³; NIST (accessed October 4, 2026)).
Where to find each number on your bill
- Billing days: the service dates or “days in period.” Two bills a month apart can differ by several days.
- Usage: the difference between the previous and current meter reads, in your utility’s unit. Many utilities bill in CCF or gallons (EPA WaterSense (accessed October 4, 2026)).
- Water and sewer usage $: the volume (per-unit) charges. EPA notes many utilities combine a fixed (base) fee with a variable (volume) fee, and many have one meter and charge sewer on the water entering the house (EPA WaterSense (accessed October 4, 2026)).
- Fixed / base $: base, meter or service charges that do not change with usage. A charge billed with zero usage belongs here.
- Other fees $: stormwater, drainage, garbage, taxes or surcharges.
- Adjustments $: credits (type a minus sign), carry-over balances and estimated-read true-ups.
FAQ
My bill doubled but I don’t have a leak. What else could it be?
Look at the bars. If usage per day is flat, the increase is price, days or fees, not water. If usage per day rose, common non-leak reasons are outdoor watering, guests and seasonal use; Seattle Public Utilities lists visitors, gardens and lawns, pools and hot tubs as places water goes (SPU (accessed October 4, 2026)).
Does a big “rate or tier” bar mean my utility raised prices?
Not necessarily. Under increasing block rates each block of use costs more than the one before (EPA (accessed October 4, 2026)), so using more water can raise your average price with no rate change. Compare the rate table on both bills to tell the two apart.
Why is sewer its own bar?
Sewer is often billed on your water use, so it moves with water. Seattle Public Utilities says sewer charges are based on water used in the period and the sewer rate is significantly more expensive than water (SPU (accessed October 4, 2026)). “Show the math” splits the sewer bar into days, usage per day and rate too.
What if one of the bills was an estimated read?
Tick “Estimated read?” If an estimate was too low, the next actual read bills the difference, so that bill looks high even though you were only catching up (SPU (accessed October 4, 2026)).
Why not just compare the totals?
Totals mix four things: how many days, how much water a day, the price of that water, and flat charges. The split shows how much of the change came from each, in dollars.
Do you keep my numbers?
No sign-up, no account. With JavaScript on, the math runs in your browser. Without it, the button puts the numbers in the page address so the server can draw the same chart.
Recap
- Put your normal bill in A and the high bill in B. The bars add up exactly to the difference.
- Usage per day up by half or more: run the two-hour meter test (EPA (accessed October 4, 2026)) before anything else.
- Usage per day flat: the cause is days, price, sewer or fees, and the rate table on your bill will show which.
Suspect the meter itself rather than your usage? That is a separate question (an “is my water meter wrong” check); start with the two-hour meter test on the leak check. Prefer to upload the PDF? Analyze the bill. Background: why is my water bill so high.
Sources
- EPA WaterSense, “Understanding Your Water Bill”: https://www.epa.gov/watersense/understanding-your-water-bill (accessed October 4, 2026)
- NIST, “SP 811 Appendix B.8, conversion factors”: https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b8 (accessed October 4, 2026)
- Seattle Public Utilities, “My Bill Seems Too High”: https://www.seattle.gov/utilities/your-services/accounts-and-payments/bills-and-payments/my-bill-seems-too-high (accessed October 4, 2026)
- EPA WaterSense, “Fix a Leak Week”: https://www.epa.gov/watersense/fix-leak-week (accessed October 4, 2026)
The split itself is arithmetic on the numbers you type; it does not use any utility’s rates. The 30-day figure is an estimate and is labeled as one.
Usage per day went up%PCT%. Rule out a leak first: EPA says to read your meter before and after a two-hour period with no water use; if it moves at all, you probably have a leak (EPA WaterSense (accessed October 4, 2026)).
No leak? Look outside next: irrigation timer spikes and outdoor watering.
Your price per gallon moved more than your usage did. That is a rate change, a higher tier, or sewer pricing, not a leak. Seattle, for example, bills water on summer tiers, so the same use costs more in summer (Seattle Public Utilities (accessed October 4, 2026)).
Read how tiers and sewer stack
Also: why sewer is higher than water, winter sewer averaging, staying under the next tier.
Mostly a longer bill. More days means more water at the same daily habit. Nothing to fix; compare the per-day numbers above.
Still want a second look? Upload the bill for a line-by-line read.
A fixed charge or fee changed. Look for a new rate year, a stormwater or drainage line, or a surcharge on bill B.
A credit, carry-over or true-up changed. Check the adjustments line on both bills before anything else.
Nothing moved enough to chase. If something still looks off, upload the bill for a line-by-line read.
One bill was an estimated read. If an estimate came in low, the next actual read bills the difference, which can make that bill look high (Seattle Public Utilities (accessed October 4, 2026)). See estimated meter read true-up.