A building can use water long after the last person leaves. Irrigation, cleaning and mechanical equipment may run on their own schedules. Start by comparing the main meter with what was actually running. The meter can show that water passed through it, but it cannot tell you which branch used it.
Compare the main meter with the operating schedule
Choose a quiet period and record the main meter’s start and end readings, units and times. If interval data are available, check whether the pattern is a short burst or steady flow. Compare that timing with cleaning, irrigation and other known uses. Verify when equipment actually operated rather than relying only on calendar settings. A missing interval belongs in the record as unknown.
Use the EPA WaterSense facility guidance to plan an off-peak review and choose where submetering would answer a specific question. Work with the responsible facilities staff; do not interrupt protective systems or essential services to create a quiet test window.
Illustrative example: one expected burst and one unexplained interval
These invented readings show how a facilities team might narrow its investigation. The volumes are examples, not leak thresholds.
| Window | Main meter | What to check |
|---|---|---|
| 10–11 p.m. | 120 gal added | Cleaning was logged. Verify the time and compare with another cleaning shift. |
| Midnight–1 a.m. | 36 gal added | No use was logged. Check the actual irrigation and mechanical equipment schedules. |
| 1–2 a.m. | No valid interval | Check the meter feed. Do not report zero use. |
Choose a branch measurement or a local water sensor
Use a submeter when the remaining question is how much water a particular branch uses and when. Use a sensing rope when the question is whether water has reached a particular floor area, such as a vulnerable spot near a riser. A dry rope does not clear a branch of leaks, and a wet rope does not identify the source or measure how much water escaped. Use the two readings together only where their locations and timing support that interpretation.
Make the next investigation repeatable
- Record the meter identity, units, interval and timestamp source.
- Compare like-for-like nights, including weather and verified operating schedules where relevant.
- Assign an owner to investigate recurring unexplained use and mark what was found.
- Verify meter and sensor coverage, including what a lost connection looks like, before relying on alerts.
See equipment monitoring for a first monitoring plan and embedded systems for equipment monitoring for installations that need a different sensing or communications arrangement.