A falling swimming-pool level can come from evaporation, splashing, cleaning or a leak. Before buying sealant or running an automatic refill indefinitely, compare the pool's loss with water exposed to the same weather in a bucket.
EPA's pool-water-efficiency guide describes a bucket comparison as a way to investigate possible leaks. It is a screening observation, not a way to locate a crack or certify that the pool is safe to use.
Check what could change the level
Record recent weather, swimming, backwashing or cleaning and any water you added. If an automatic refill is operating, it can hide the level change you're trying to observe. Use the equipment instructions or a pool professional to arrange a valid comparison.
From a safe dry position, look for visible water around accessible pool equipment and unusual wet ground. Don't open electrical equipment or pressure vessels. A wet area is useful information, but it doesn't identify a buried pipe as the cause by itself.
If the loss is rapid, the structure appears damaged or water is near electrical equipment, arrange professional assessment promptly. Don't keep operating the system to complete a test when conditions appear unsafe.
EPA's bucket comparison
The EPA guide describes turning off pool equipment for its test. Only use controls you can operate safely and follow the exact equipment instructions. If you're unsure about shutting down or preventing automatic operation, have a pool professional handle the setup.
Fill a 2.5- to 5-gallon bucket about three-quarters full. Place it securely on a pool bench or step so part of the bucket is submerged and the water inside sits a little above the surrounding pool level. Don't enter an unsafe pool to position it, and keep children and animals away from the unattended setup.
Mark the starting bucket-water level and record the starting pool-water level against a fixed reference. EPA says to leave the bucket for 24 hours, then record both levels again. Compare the amount of drop in each, rather than comparing their final heights.
If the pool loses more water than the bucket, EPA says the pool may have a leak. The comparison doesn't tell you where the leak is or which repair is appropriate.
Keep interruptions with the observation
| Observation | What it tells you |
|---|---|
| Pool drops more than the bucket | A possible leak warrants further investigation. It does not locate the fault. |
| Similar drops | Evaporation may account for the observation. It does not rule out every intermittent fault. |
| Rain, refill, splashing or tipped bucket | The comparison may be unreliable. Record the interruption before interpreting it. |
Rain, added water, swimming, splashing or a tipped bucket can affect the comparison. Record those events. If they make the observation unreliable, ask a professional how to repeat it under suitable conditions rather than presenting the numbers as a clean test.
A useful note includes the start and end times, weather, equipment state, refill status and both measured drops. Don't call every difference a confirmed leak or assume similar drops rule out every intermittent fault.
Keep routine pool-water testing separate from the level comparison. The pool strips versus DPD guide helps you choose a suitable test method and record a result you can interpret.
Work through the comparison without guessing
Use the same units for the pool and bucket. If you measure the distance down from a fixed reference, that distance will increase as the water falls. Write down both the starting and finishing distances so you don’t accidentally describe a larger gap as a rising water level.
For a hypothetical example, suppose the pool drops half an inch while the bucket drops a quarter of an inch during an uninterrupted observation. The pool’s drop is greater, which fits EPA’s reason to investigate a possible leak. It doesn’t prove that exactly a quarter inch leaked from a particular pipe. The comparison is a screening tool, and measurement conditions still matter.
Now imagine a second observation in which both drop about a quarter inch. That is more consistent with evaporation accounting for that observation. It isn’t a certificate that the pool never leaks. A fault that happens only under different operating conditions may need a professional’s separate test.
A water-loss worksheet you can save
Use this as a notebook checklist or copy the rows into a spreadsheet. Leave a field blank when you didn’t observe it. Don’t reconstruct missing details later just to make the record look complete.
| Record | Your observation |
|---|---|
| Start and finish date and time | Record both, including the actual elapsed period. |
| Pool starting and ending readings | Use one fixed reference and the same units. |
| Bucket starting and ending readings | Keep its reference unchanged. |
| Equipment and refill state | Note the safely established setup and any automatic operation. |
| Weather and pool use | Record rain, wind changes, swimming or splashing. |
| Added or discharged water | Note refilling, cleaning and any interruption. |
| Visible observations | Describe accessible wet areas or changes without naming an unconfirmed fault. |
Photograph the marks if you can do so safely without entering the water or leaning over an unsafe edge. Include the reference in the photograph. Two close-up water pictures without a reference may be attractive, but they won’t help someone compare the readings.
Turn a level change into a rough quantity
A water-level change can be easier to understand when expressed as volume. For a rectangular pool, surface area multiplied by the vertical drop gives an approximate lost volume. Use the water surface’s dimensions rather than the outside dimensions of the deck.
Here is an arithmetic example, not a measured pool result. A rectangular water surface 15 feet wide and 30 feet long covers 450 square feet. A half-inch drop is about 0.0417 feet. Multiplying gives about 18.75 cubic feet, or roughly 140 US gallons using about 7.48 gallons per cubic foot.
That estimates the total drop during the observation, not the amount attributable to a leak. Evaporation, splashing or cleaning may contribute. Curved, irregular or changing-width surfaces need a suitable area estimate, so don’t present this rectangle example as an exact calculation for every pool.
If you want to estimate the water bill, use your actual utility’s applicable volume charge and units. Check whether sewer charges, tiers or fixed charges affect the calculation. A generic national price won’t tell you what your refill costs.
Get a repair proposal that names the work
Ask whether the initial visit covers diagnosis, repair or both. A leak-detection fee and a repair quotation may describe different services. Find out which accessible equipment and which concealed areas are included before comparing two prices.
Request a written description of the confirmed problem, the proposed method, any access or surface restoration and the follow-up check. Ask who will arrange any required permits or specialist work. Don’t assume that a lower quote includes the same scope or that the most expensive quote identifies the correct fault.
After work is complete, keep the provider’s findings with your original observations. Agree on how the repair will be checked under the appropriate conditions. A pool that has just been topped up doesn’t by itself demonstrate that water loss has stopped.
What to give the repair provider
Send the observation record, accessible photographs and any recent equipment-service history. Explain whether water loss appears constant or was noticed after a particular operating change. Let the provider decide which further checks are appropriate.
Don't drain the pool, enter suction fittings, dismantle a pump or add an unknown leak-sealing chemical based on this comparison. Structural, plumbing, electrical and equipment repairs need the right diagnosis and procedure.
Ask for the proposed repair and the follow-up check in writing. The aim is to resolve the cause, not only restore the visible water level.
Reduce evaporation without confusing it with safety
EPA describes pool covers as a useful way to reduce evaporation when they are used. It also distinguishes safety covers from products such as bubble covers that aren't safety covers. Don't treat an evaporation product as a substitute for compliant barriers, supervision or other pool-safety requirements.
Keep pool records separately from drinking-water records. A pool level comparison is unrelated to whether water is safe to drink, and adding fresh water doesn't establish appropriate swimming-water quality.
Once you have recorded a suitable observation, use the pool water-loss calculator to compare the drops. A rectangular surface estimate shows total volume change, not a confirmed leak rate.
For ordinary evaporation control, compare pool-cover fit, use and safety documentation. Keep filter backwashing and refill events in a separate service record so intentional discharge is not mistaken for unexplained loss.
To budget for a documented refill, use the pool refill cost calculator with your actual applicable utility rates. It estimates usage charges and does not identify the cause of water loss.
