How do I calculate how much water a leak wastes?

Measure or estimate the leak flow, then multiply it by the minutes the leak runs. This calculator converts drip count, known flow, or a timed container test into a common litres-per-minute rate before applying the leak schedule.

How much water does one drip per second waste?

Using the USGS planning assumption of 0.25 millilitre per drip, one drip per second wastes about 21.6 litres, or 5.7 US gallons, per day. Real faucet drops vary, so a timed container test is more accurate.

Does the cost include sewer charges?

Only if the rate you enter includes them. Use the variable combined water and wastewater rate from your bill when both charges rise with metered use. Fixed charges are not avoided by fixing a leak.

Can I estimate a toilet leak?

Yes. Use a known or estimated flow rate, or select an EPA example preset. Toilet leaks can be silent and variable, so confirm the leak with a dye test, meter observation, or qualified plumber.

Are my leak and bill details uploaded?

No. All calculations run locally in your browser; this tool does not send or store the values you enter.

Home Water Leak Waste & Cost Calculator

Estimate wasted water and variable utility charges from a dripping faucet, leaking toilet, pipe, hose, or irrigation fault. Your inputs stay in your browser.

Leak details

1. How did you measure the leak?

Counted drips Known flow rate Container test

Drips per minute Count for a full minute when practical. Estimated drop size

USGS uses 0.25 mL as a planning estimate; real drops vary.

2. How often does it leak?

Hours per active day Use 24 for a continuous leak. Active days per week Use 7 if it leaks every day.

Projection period Period unit

3. What does metered water cost?

Currency Variable utility rate Editable example. Include sewer only if billed by usage. Billing unit

Use only charges that change with consumption. Fixed service, meter, and minimum charges normally remain after a repair.

Planning estimate only. Leak flow can change with pressure and fixture position. Confirm unexpected use with your meter or utility and arrange an appropriate repair.

Estimated waste and cost

Using the slow faucet drip example.

How the leak calculation works

Drip method: litres/min = drips/min × mL/drop ÷ 1,000.
Container method: litres/min = collected litres ÷ seconds × 60.
Scheduled daily waste: litres/min × 60 × hours/day × active days/week ÷ 7.
Projected variable cost: projected volume ÷ billing volume × rate.

One US liquid gallon is 3.785411784 litres. A month is represented as 365 ÷ 12, or about 30.44 days; the dedicated 30-day result uses exactly 30 days.

The drip method is useful for a quick estimate, but droplet size is not standardized. A timed container test or meter-derived flow is usually more representative. For intermittent leaks, the calculator spreads active leak time across the week to show an average day.

Water-damage limit: this calculator estimates consumption and variable utility cost, not property damage. If water is spreading, near electrical equipment, affecting a ceiling, or cannot be isolated safely, treat the leak as urgent and contact the appropriate emergency or qualified professional service.

Sources, assumptions, and limits

Last reviewed: August 3, 2026

Drip-volume assumption: the USGS Water Science School drip calculator uses 0.25 mL per faucet drip, while noting that there is no scientific standard for faucet-drop volume. That value is the editable default here.
Leak examples: EPA WaterSense potential water-loss examples list a small leaking toilet at 0.02 gpm and a medium leak at 0.2 gpm. These are illustrative presets, not diagnoses.
Why leaks matter: EPA WaterSense Fix a Leak Week reports more than 9,300 gallons of annual waste for an average household’s leaks and says 9% of homes have leaks wasting at least 50 gallons per day.
Cost scope: results include only the usage rate entered. Tiered pricing, taxes, drought surcharges, minimum bills, fixed charges, hot-water energy, repair cost, and damage are excluded.

FAQ

How do I measure a leak with a cup?

Place a container under the leak, collect water for a measured number of seconds, and enter both the volume and time. Use a longer interval for very slow leaks. Do not attempt a container test where access is unsafe or could spread water.

How much does one drip per second waste?

With the editable USGS assumption of 0.25 mL per drip, 60 drips per minute wastes about 21.6 litres, or 5.7 US gallons, per day. Actual drops vary, which is why this figure may differ from general leak-awareness examples.

Can I use readings from my water meter?

Yes. Turn off intentional water uses, observe the volume change over a known time, convert that difference to a rate, and select “Known flow rate.” Follow your utility’s meter-reading instructions and do not access sealed or unsafe equipment.

Why is my calculated cost different from my bill?

Many bills use tiers, seasonal rates, separate wastewater rules, taxes, fixed charges, or minimum charges. Enter the marginal rate that applies to the extra leak consumption. The calculator cannot reproduce charges you do not enter.

Should sewer cost be included?

Include the wastewater rate if your sewer charge is based on metered water use and would decrease after the leak is fixed. Exclude it when the charge is fixed, capped, separately metered, or adjusted by another method.

How can I check for a silent toilet leak?

EPA WaterSense suggests placing a few drops of food coloring in the toilet tank and checking the bowl before flushing. Follow current EPA or local utility instructions for the waiting period and cleanup.

Does this calculator track my bill or leak details?

No. The calculation, copy action, and text-file download happen locally in your browser. Values are not placed in the URL or sent to Starlight Tools.

Home Water Leak Waste & Cost Calculator

Leak details

1. How did you measure the leak?

2. How often does it leak?

3. What does metered water cost?

Estimated waste and cost

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How the leak calculation works

Sources, assumptions, and limits

FAQ

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