A falling pool level does not identify the cause by itself. Evaporation, splash-out, cleaning, refills and leaks can all affect what you observe. A water loss log helps you describe the pattern without turning one measurement into a diagnosis.
Record the same reference point each time
Choose a safely visible fixed point and record how far the water surface sits below it, using one unit throughout. Note the time as well as the date. If the point moves or cannot be read consistently, mark the reading as uncertain. Do not lean over an unsafe edge or enter the water to obtain a measurement.
Use a sign convention that you can explain. In this worksheet, a larger distance below the reference means a lower water level. For example, an illustrative change from 2.0 inches below the point to 2.3 inches below it means a 0.3-inch net drop. That is a change in level, not a measured leak rate.
Capture the events that make a comparison misleading
| Field | Record | Why it matters |
|---|---|---|
| Time interval | Start and finish time | A 12-hour observation and a 24-hour observation differ. |
| Weather | Rain, wind and major temperature changes | Outdoor conditions affect the comparison. |
| Pool use | Swimming, cleaning or unusual splashing | Water can leave without a leak. |
| Cover and features | Whether a suitable cover or water feature was in use | Changing conditions can change losses. |
| Water added | Known refill event and measured amount if available | An autofill may hide a falling level. |
| Water removed | Backwash or other authorized discharge | Known removal is not unexplained loss. |
| Equipment observation | Safely visible damp area or drip; time noticed | Provides a location and timing to discuss. |
If an automatic refill operates but its volume is unknown, mark that period as affected by unknown added water. Do not write zero. If a whole-house meter is used, other household consumption prevents assigning the entire difference to the pool. A dedicated, correctly interpreted supply meter can provide a clearer record.
Separate net change from gross water loss
The observed level change is the result after additions and removals. Rain or refilling can offset loss. A nearly unchanged level therefore does not prove that no water is leaving. Conversely, a visible drop after filter backwashing does not establish a leak. Keep the events beside the measurement rather than correcting the number with a guessed allowance.
EPA WaterSense identifies evaporation, pool cleaning, leaks and splashing as sources of pool water use. Its pool-efficiency guidance is a useful starting point for maintenance discussions. This article deliberately does not set a universal inches-per-day threshold: local conditions and pool operation matter.
Know when a log should not delay help
Seek qualified help promptly for a rapid or unexplained change, visible damage, a suspected underground leak, unsafe equipment or water levels that may compromise normal operation. Keep people away from an area that appears unsafe. Do not keep equipment operating outside its manual’s requirements just to finish an observation period.
Do not drain the pool, close unfamiliar valves, bypass an autofill or shut down required equipment as an experiment based on this article. A professional can specify a suitable diagnostic method for the system. If they request a controlled observation or bucket comparison, ask for the exact setup, operating conditions and stop criteria rather than combining unrelated online instructions.
Send a concise record to the provider
- State when the change was first noticed and whether it is ongoing.
- Share consecutive readings with units and times.
- Highlight rain, swimming, refills and discharge events.
- Include the equipment model and relevant maintenance history.
- Describe visible observations without calling them a confirmed leak location.
- List any information you could not measure reliably.
Ask what the inspection covers, whether diagnosis and repair are separate charges, and what evidence would support a proposed repair. Keep a copy of the findings next to the log. Use the repair-preparation checklist to compare the written scope.
Frequently asked questions
How much water loss is normal?
There is no universal allowance that this log can establish. Evaporation and other losses depend on conditions; discuss the recorded pattern with a qualified provider.
Does a bucket test prove the location of a leak?
No. A comparison can support further investigation under suitable conditions, but it does not locate a fault or replace professional diagnosis.
Should I turn off the autofill?
This guide does not instruct equipment changes. Ask a qualified provider how to observe your system while maintaining the required water level and safe operation.
Can I convert a level drop into gallons?
That requires a reliable water-surface area and appropriate geometry. Even then, the net volume change is not automatically the volume lost through a leak.
Source and limits
The worksheet and arithmetic example were prepared by Poolside. EPA’s general water-use guidance was checked October 23, 2026. No site-specific evaporation model, leak inspection or field measurement is claimed.
Poolside creates practical worksheets and explanations for pool owners. These resources were prepared with AI assistance using the references listed in each article. Examples are illustrative; no field testing or independent technician review is claimed.
More Poolside guides →
