Estimate how much water a dripping faucet or leak wastes per day, month and year from drips per minute or measured flow, with optional water cost.
Water Drip Formula
Use counted drips, a measured per-fixture flow rate, or a known total daily loss. Enter the number of similar fixtures and actual active hours (greater than zero, up to 24). The default EPA worksheet scenario assumes 10,000 drips per US gallon. The separate 0.25 mL/drop scenario uses that volume exactly, or you can enter a measured drop volume.
When the leak is measured directly as a flow rate instead of counted as individual drips, use these conversions:
If you already know the total daily leak and want to estimate the average drip rate per faucet, rearrange the main formula:
Variable Definitions
- WLgal/day
- Total water lost in gallons per day.
- WLL/day
- Total water lost in liters per day.
- Dmin
- Average drip rate in drips per minute for each leaking faucet.
- Qgal/min
- Measured leak flow rate in gallons per minute.
- QL/min
- Measured leak flow rate in liters per minute.
- F
- Number of dripping faucets.
- 1440
- Minutes in one day.
- Drop-size model
- EPA worksheet: 10,000 drips per US gallon. A 0.25 mL/drop assumption instead gives 15,141.647136 drips per US gallon using the exact gallon conversion. Real drop volumes vary; neither is a universal constant.
How to Use the Calculator
- Choose drip loss, reverse drip rate, or measured flow mode. Count similar leaking fixtures and enter their active hours.
- If the leak is dripping, count the number of drips in 60 seconds and repeat the test a few times to get a reliable average.
- Enter the visible required rate or total daily loss. In drip modes, choose the EPA worksheet, 0.25 mL/drop, or measured-drop scenario.
- For a trickle, use measured-flow mode with the flow per fixture. Collect a known volume over a measured time; no drop assumption is used.
- Read the total daily water loss, then extend it to weekly, monthly, or yearly usage if needed.
If different faucets leak at different rates, the most accurate approach is to measure each faucet separately and add the totals. If they are similar, you can use the average drip rate per faucet and multiply by the number of leaking faucets.
Example
Suppose 4 similar faucets each drip 25 times per minute for 24 hours per day. Select the EPA worksheet assumption of 10,000 drips per US gallon:
That scenario gives 100.8 US gallons per week, 432 in 30 days, 438 per average month (365 ÷ 12 days), and 5,256 per 365-day year. The periods assume the same rate throughout; they are not a calendar-month or leap-year forecast.
Quick Leak Reference
One fixture, 24 active hours per day, EPA worksheet assumption of 10,000 drips per US gallon and a 365-day year:
| Drip Rate per Faucet | Approx. Gallons per Day | Approx. Gallons per Year |
|---|---|---|
| 1 drip/min | 0.14 | 52.56 |
| 10 drips/min | 1.44 | 525.60 |
| 30 drips/min | 4.32 | 1,576.80 |
| 60 drips/min | 8.64 | 3,153.60 |
| 120 drips/min | 17.28 | 6,307.20 |
For multiple faucets with similar leak rates, multiply the daily or yearly amount in the table by the number of leaking faucets.
Why Real-World Results May Differ
- Drop size is not perfectly constant, so actual gallons lost can vary from the estimate.
- Water pressure, faucet design, and aerator condition can change the volume of each drip.
- A leak that alternates between dripping and streaming should be measured as flow rate rather than drips per minute.
- Intermittent leaks only waste water while they are active, so time-based estimates are most accurate when the leak is continuous.
Estimating the Cost of a Leak
If your water bill is based on usage per 1,000 gallons, you can estimate the monthly cost of a leak with the formula below:
Enter the combined variable water and applicable sewer rate in the currency used by your bill. Blank means cost not requested; zero is a zero rate. Fixed fees, tier changes, sewer caps and hot-water energy costs are excluded, so the estimate is not a guaranteed bill saving.
