How Much Will Filling a Pool Raise Your Water Bill?

Filling a pool from the tap usually puts every gallon on one billing cycle, and the water bill pool owners get that month goes up for three separate reasons: the water itself, the higher price tier a big month pushes you into, and the sewer charge many utilities bill on the same gallons. Nobody can give you the exact figure without your own rate sheet, because water and sewer prices vary widely, even between utilities a few miles apart. What you can do is the arithmetic, using the sample bill below, and then take the steps that make the number smaller.

For the whole comparison of hose, tanker and well, see the full cost guide. This page sticks to what your meter and your bill do.

The formula: gallons divided by 1,000 times your rate

Utilities bill water in one of two units. Some charge per 1,000 gallons, shown as "kgal" or "per thousand" on the bill. Others charge per CCF, which is one hundred cubic feet or 748 gallons, and the bill may call it HCF or just "units".

Per 1,000 gallons: pool gallons ÷ 1,000 x rate = water charge for the fill.

Per CCF: pool gallons ÷ 748 x rate = water charge for the fill.

A 20,000-gallon pool is 20 thousand-gallon units, or 26.7 CCF. Multiply your unit price by 20 (or by 26.7) and you have the water part of the increase at your base rate. Tiers and sewer come on top of that, and together they can add more than the base figure itself.

You need the gallons first. For a rectangle that's length x width x average depth x 7.5, all in feet, with the depth measured to the water line. The cost by pool size guide lists the common shapes.

Where to find your rate per 1,000 gallons

Your last bill usually shows it, though not always clearly. Look for a usage line with a unit price next to it, separate from the fixed service or meter charge. The fixed charge stays the same when you fill a pool, and only the per-unit lines move.

If the bill only shows a total, search for your utility's name plus "rate schedule". From the tariff you want the water rate and its tiers, the sewer rate and what it's based on, and any seasonal or drought surcharge, along with the usage level it starts at if it has one.

Tiered rates: why the last gallons of a fill cost the most

Many US utilities sell residential water in inclining blocks. The first block of gallons each month costs the least, the next costs more, and anything above that costs the most. The idea is to reward low use, so a month with a pool fill in it gets billed at the expensive end of the scale.

Take an example where the first 5,000 gallons a month are billed at tier 1, the next 10,000 at tier 2, and everything over 15,000 at tier 3. A normal month of 6,000 gallons is 5,000 at tier 1 and 1,000 at tier 2. The fill month is 26,000 gallons: 5,000 at tier 1, 10,000 at tier 2, and 11,000 at tier 3, the most expensive water the utility sells.

So the pool wasn't billed at your usual rate. Of the 20,000 extra gallons, 11,000 went in at the top rate, 9,000 at tier 2, and none at tier 1.

Sewer charges are the hidden half

Houses don't have a sewer meter. Utilities that bill sewer by volume base it on the water meter, on the assumption that what comes in goes down the drain. Pool water doesn't, but the meter can't tell the difference.

Sewer rates per unit are often similar to water rates and in some cities higher, so the real increase can be double the water line or more. Check your tariff for two things.

The first is winter averaging. Some utilities set your sewer charge from your average water use over a few winter months. If yours does, a summer fill doesn't touch the sewer line, while a fill during the averaging months can raise it for the whole period that average covers.

The second is a pool-fill sewer credit. Some utilities will take the sewer charge off a one-time fill, and many want to hear from you before you start. You may be asked for meter readings before and after, or for a form. Others don't offer a credit at all, so call and ask. The sewer credit for a pool fill guide covers what to say and what to have ready.

A sample bill before and after a 20,000-gallon fill

This bill is hypothetical. The letters stand for the figures on your own tariff: F is the fixed charge, W1, W2 and W3 are the water tiers per 1,000 gallons, and S is the sewer rate per 1,000 gallons of metered water. The tiers are the example ones above, so write your own numbers in and multiply.

Most people expect the increase to be 20 x W1. It's more than that because none of the pool water landed in tier 1, and unless you got the credit, the sewer term adds a second charge on all 20,000 gallons.

To see how far off that guess is, put the tiers in proportion. If tier 2 is 1.5 times tier 1, tier 3 is twice tier 1, and sewer equals tier 1, the increase is 13.5 x W1 + 22 x W1 + 20 x W1 = 55.5 x W1, nearly three times the 20 x W1 you expected. With a sewer credit it drops to 35.5 x W1. On a flat-rate utility, the increase is simply 20 x W + 20 x S.

Ways to keep the bill down

1. Ask for the sewer credit before the first gallon goes in. Where it's offered, it's usually the biggest saving on the bill, and some utilities won't apply it after the fact.
2. Pick the month. If your utility uses winter averaging, fill outside those months, and avoid its seasonal summer rates if it has them.
3. On an existing finish only, split the fill across the meter-read date. With 10,000 gallons in each of two cycles, the example tiers put about 1,000 gallons a month in tier 3 instead of 11,000. Never do this on new plaster or pebble, which needs one continuous fill.
4. Truck part of it. One or two tanker loads take 6,000 to 16,000 gallons off the meter, and the hose finishes the rest, mostly in the lower tiers. A tanker load usually costs more than the same water from the tap, so run your tariff numbers first.
5. Check restrictions first. During droughts some areas ban or limit filling pools from the tap, and a fine would cost more than the water.

When a truck beats the tap

On city water the hose is usually cheaper per gallon, and we say so in our hose versus trucked water comparison. A truck starts to make sense in a few situations. A steep top tier and a high sewer rate with no credit push the tap cost well past the simple guess, which narrows the gap. A truck is usually done the same day, while a 20,000-gallon pool takes about 33 to 67 hours by hose at 5 to 10 gallons a minute. On a private well, a full fill can run the pump for a day or more and strain the well. New plaster needs a fill that doesn't stop, and in some places filling from the tap is restricted.

An in-ground pool usually takes 2 to 5 loads, and the in-ground pool fill page explains how the day works. Your quote gives the exact delivered price.

Frequently asked questions

Does filling a pool increase your water bill a lot?

For most households it's the biggest single month on the account, because 15,000 to 30,000 extra gallons land in one cycle and much of that is billed at your top tier. The size of the jump depends on your utility's rates, so run the sample bill with your own tariff rather than trusting a national average.

Will my sewer bill go up if I fill my pool?

If your utility bills sewer on metered water and doesn't use winter averaging, yes, by the same number of units as the water. Ask about a pool-fill sewer credit before you start, since some utilities only grant one if you ask first.

Can I get a pool fill credit on my water bill?

Usually only on the sewer part. The water went through your meter and you pay for it, and the sewer credit exists because that water never reached the drain. Call your utility, ask for the pool-fill or sewer-adjustment process, and take a meter reading before and after the fill.

Is there a cheaper time of year to fill a pool from the tap?

Often, yes. Avoid your utility's winter-averaging months, its seasonal summer rates and any drought surcharge. Depending on your tariff's dates, that often points to late spring or early fall.

Rather not find out on next month's bill? Tell us the ZIP and the gallons and a person sends one delivered price for the same water, usually within 1 to 2 business hours, to set next to your own math. See your delivered price.