Water Bill Calculator

A water bill is three charges, not one

Water arrives as a base charge, a usage charge and a sewer charge, and only the middle one moves with the meter. The base charge is what the utility bills for having a connection at all. The usage charge is the gallons priced through one or more rate blocks. The sewer charge is usually priced on the same gallons a second time, because most utilities bill wastewater on the volume of water that came in rather than metering it separately. A page that multiplies gallons by one rate is wrong on all three counts.

Where each number comes from on your own bill

The gallons are in the meter-reading block: present reading minus previous reading, multiplied by any meter multiplier printed beside it. If your meter is read in cubic metres, one cubic metre is 264.172 gallons; if the bill is in hundreds of cubic feet, one hundred cubic feet is 748.05 gallons. Those conversions are exact, but the tier boundaries on a metric bill are not the same round numbers as on a US one, so convert the rate rather than the block.

The base charge goes by several names: service charge, customer charge, readiness-to-serve, minimum bill. The block rates are on the rate schedule, quoted per 1,000 gallons or per 100 cubic feet. The sewer rate is usually a separate line priced per 1,000 gallons of water used, and it is the line that surprises people, because it is charged on water that never reaches the sewer if it went on a garden.

The base charge is a floor you cannot use your way out of

On the example rate card in the fields above, the first 1,000 gallons cost $19.80 all in and the third 1,000 gallons cost $8.95. That is not a volume discount. The water rate for the first block is the same $3.20 either way; what changed is how much base charge is riding on each thousand gallons. At 1,000 gallons the $12.50 adds $12.50 to every thousand. At 4,000 gallons it adds $3.13.

Two flats on the same rate card, one using 1,000 gallons and one using 4,000, are paying $19.80 and $11.25 per thousand gallons. Neither is being overcharged and neither rate is different. Comparing two bills by dividing the total by the gallons is therefore only fair at the same usage, which is why the all-in figure here is a diagnostic rather than a price.

Sewer is the half of the bill nobody quotes

Every extra 1,000 gallons is priced twice: once on the water line at the block rate and once on the sewer line. At 3,000 gallons on this card that is $4.85 + $4.10 = $8.95 for the next thousand, not $4.85. A leak that runs 1,000 gallons down the drain costs $8.95, and fixing it saves the same. This is also why a bill can look wrong when only the water rate is checked: the sewer line moves in step, and a 10% cut in gallons cuts the bill by more than 10% of the water charge, because it takes the sewer charge down with it.

The relationship breaks in two places. Some utilities cap the sewer charge at a winter average, so summer garden water is billed for water but not for sewer. Some bill wastewater on a flat assumption rather than the meter. If either applies, the sewer rate in the field above is the effective rate, and the total will match the bill only after the cap is accounted for.

Splitting it: the base charge does not shrink

Divided between three people, $36.05 is $12.02, $12.02 and $12.01 — the cent that will not divide goes to the first two, because the share is 1,201.67 cents each and the two largest remainders are identical. Between two people it is $18.03 and $18.02; between four it is $9.02, $9.01, $9.01 and $9.01. The arithmetic is the same largest-remainder rule the rest of this site uses, so the parts always sum exactly to the bill.

What does not divide evenly is the reason behind the bill. The $12.50 base charge is per connection, not per person: one person pays it alone, four pay $3.13 each. So a flat of four does not pay four times what a single renter pays for the same volume — it pays less per head before a drop is used. When the roommates' usage is uneven rather than just the headcount, the split needs a basis rather than a division; the split utilities page runs water, power, gas and internet on separate bases, and the monthly household bill page puts all five lines in one table per person. A person who joins or leaves mid-month has the same problem one level up, with rent rather than water: the prorated rent page divides a month into days the way this page divides a bill into people, and the shares sum exactly to the month.

Reading a bill backwards to check it

Take the total, subtract the sewer charge, subtract the base charge, and what is left is the usage charge. Divide that by the gallons in thousands and you get the average block rate actually paid. On the 3,000-gallon example: $36.05 minus $12.30 of sewer is $23.75, minus $12.50 of base is $11.25, and $11.25 over 3 thousand gallons is $3.75 — which sits between the $3.20 first-block rate and the $4.85 second-block rate, exactly where a 2,000/1,000 mix should sit. If the same subtraction on your own bill gives a number outside the two rates on the schedule, a block boundary, a cap or a surcharge is missing from the fields.

How a tiered (increasing-block) water rate turns usage into a bill

A flat per-gallon price is easy: gallons times rate. Most municipal systems do not charge that way — they use increasing-block (tiered) rates, where each extra slice of water costs more than the last. The first block is cheap to cover basic indoor need; each higher block is priced to discourage use. Reading the schedule is the same skill as reading this page's bill, just one level down: you must know where each block boundary falls, not just the headline rate.

The table works one illustrative three-tier card. These are example numbers set by this page, used only to show the arithmetic; they are not a state or area average and cite no source — your own card's blocks and rates will differ.

At 6,000 gallons the bill is $6.40 + $8.20 + $10.60 = $25.20 of usage charge, plus the same base and sewer this page already adds. The columns trace to sources as follows:

• Tier / block structure — the increasing-block concept (price rises with each block) is an example structure set by this page; it cites no source.
• Monthly allowance — the 2/2/overflow block sizes are example values set by this page; they cite no source.
• Rate ($/1,000 gal) — the $3.20 / $4.10 / $5.30 figures are example values set by this page; they are not a state or area average and cite no source.
• Block charge — each cell is computed by the formula in the next paragraph, not quoted from anywhere.

Collapsing a tier schedule into one effective price

One number people actually want is the effective price per 1,000 gallons across a tier schedule, so they can compare it to a flat-rate neighbour. Sum each block's (gallons in block × block rate), add the base charge, divide by total gallons. For the 6,000-gallon example: ($6.40 + $8.20 + $10.60 + $12.50 base) / 6 = $6.28 per 1,000 gallons. That is the number to put next to a flat $4.50 neighbour — the tier card looks cheaper per unit only because the first block is underpriced, and it is more expensive once usage crosses the second boundary.

The mirror question — at what usage do two different rate plans cost the same — is the break-even. Write plan A as base_A + Σ r_A,i·block_A,i(u) and plan B the same way, set them equal, and solve for u. For a two-block card that is linear in each region, so the crossing point is where the two piecewise lines meet; above it the steeper plan wins, below it the flatter base wins. No other page on this site computes that crossing, which is why it lives here.

What this page does not do

It does not know your rate card, your block boundaries beyond the two the fields allow, your sewer cap, your irrigation meter or your seasonal rates. It does not quote an average household usage, because the spread is wide enough that an average would be a worse input than the number printed on your own bill. It also does not convert units for you: enter gallons and a rate per 1,000 gallons, and if your bill is metric, convert first. Everything it does is shown line by line so the total can be rebuilt by hand.