The Invisible Slab Leak: How High-Resolution Water Data Caught 5,426 Gallons a Day

Case Study · Multifamily Property

A leak that didn't show up on the bill, until we showed it.

Most operators only see one number a month from the utility. Below, we plot daily totals (already 30× more resolution) and the slab leak is still invisible. Then we layer NOWi on top.

Peak silent loss at detection

Continuous water loss flowing through the meter, invisible at daily resolution.

5,426
gallons / day

1. The mystery: what an operator would have seen

Eight weeks of daily total water consumption at a multifamily property, April 15 through June 11. Usage drifts upward as the season warms. Nothing here would prompt a maintenance call. Nothing here would prompt a second look.

Daily total water consumption, no obvious leak signal
Read it cold A reasonable operator would call this a healthy summer ramp. No spike, no anomaly day, no flag. The leak is hiding underneath every single bar.

The trouble with daily aggregates is that they obscure the very signature that distinguishes a leak from normal life. A property uses water in bursts: showers in the morning, dishwashers at night, irrigation before dawn. Add a slow continuous loss to the bottom of that picture and the bursts still dominate. The leak is mathematically present, but visually invisible.

2. The detection: what NOWi's algorithm saw

This is the same eight weeks of data, with one addition. The blue bars are total usage, unchanged. The red overlay is NOWi's estimate of how much of each day's water never reached a fixture, partitioned out as continuous loss.

Same chart with NOWi leak detection overlay in red
Read the floor Same gallons through the meter, partitioned into intended use vs. silent loss. The leak triples through May.

Through the second half of April the loss is negligible. In early May it begins to climb. By the third week of May it has tripled. By the first week of June it sits at over five thousand gallons a day, and is still growing. This is not a model that requires the bill to spike. It is a structural observation about what water does when nobody is using it.

3. The evidence: the smoking gun lives between 2 a.m. and 4 a.m.

A healthy property runs nearly dry overnight. Zoom from daily totals into hourly resolution and the leak announces itself as a rising overnight floor: continuous, monotonic, indifferent to time of day.

Hourly water usage clearly showing the rising overnight baseline that indicates a leak
The diagnosis is shape Diurnal spikes are normal life. The continuously rising floor underneath them is not. No seasonal trend, irrigation schedule, or resident behavior produces a steadily climbing 3 a.m. baseline. By late May the leak alone is using more water at 3 a.m. than the entire property used on a quiet April Sunday.

And remember, most operators don't even get this view. Their utility bill arrives once a month as a single number. If a slab leak hides inside daily data this well, it disappears entirely inside monthly data, typically until drywall is wet, mold has started, or the bill quietly doubles.

By the numbers

Peak loss

5,426

gallons / day at detection

Annualized waste

~1.98M

gallons / year if untreated

Avoided utility cost

~$23.8K

est. water + sewer / year

Three takeaways for property operators

1

Resolution beats volume.

A 5,000 gal/day loss is invisible inside 12,000 gal of legitimate use. Hourly data makes the same loss obvious within days.

2

The floor is the tell.

Every property has an overnight minimum. When it rises night over night without explanation, the property is leaking.

3

Lead time pays for itself.

The biggest savings aren't gallons. They're avoided drywall, mold remediation, insurance claims, and unit-days offline.

Want this kind of visibility on your portfolio?

NOWi watches every property continuously, with the same algorithm that caught this leak.

contact@nowisensors.com  ·  860.234.6779  ·  nowisensors.com