How Continuous Monitoring Caught a $2,500 a Month Boiler Leak

On August 12, a boiler in a multifamily building we monitor started leaking. Nobody saw water. Nothing flooded. No resident called it in. The building ran exactly as it always had, and the only trace was a line on a chart that stopped going back down at night.

Fourteen days later the maintenance team had it fixed. Left alone, it would have cost the owner about $30,000 a year.

The short version

What the data showed

The chart above is the building's water usage for the month of August. The blue line is total consumption. The red band underneath it is continuous flow, the portion of usage that never stops, which is what a leak looks like in the data.

Before August 12, that red band sits near the floor. Every building has a little of it. Then it steps up to roughly 160 gallons an hour and stays flat for two solid weeks. Flat is the tell. Residents do not use water at a constant rate at 3 a.m. Equipment does.

On August 26 the band drops off a cliff and the building returns to its normal daily rhythm. That is the moment the repair happened, visible in the data within the hour.

Why nobody noticed

This is the part owners tend to find frustrating. A boiler leak that drains cleanly to a floor drain produces no symptom anyone can act on. There is no puddle, no stain, no ceiling damage, no resident complaint. The building's heating still works. Nothing is visibly broken.

The only conventional signal is the water bill, and that arrives weeks after the fact as a single number with no explanation. By the time somebody notices the bill looks high, questions it, and sends a tech to walk the property, months have usually gone by. Two months of this leak would have paid for the monitoring hardware several times over.

This is the same pattern we found across a 47-building Los Angeles portfolio, where nearly three in four buildings were leaking on day one and none of the owners knew.

What actually made the difference

Nothing exotic. A single strap-on monitor on the building's main line, no plumbing cuts, no shutoff, no electrician. It reports usage continuously and flags sustained flow that never returns to zero. The alert went to the property team, they knew to look at mechanical rather than chasing units, and they found the boiler.

The value here is not the sensor. It is that the problem became a work order in days rather than a line item on a bill six months later. A leak you can see is a leak you can schedule.

If your buildings look fine, check anyway

Buildings that seem fine are exactly the ones this happens to. There is no way to rule out a continuous leak by walking a property, because the ones that matter most are the ones that make no mess. You need to see the overnight floor, and you need to see it every day.

Start with a handful of buildings, or the ones with water bills that never quite add up. Devices install in seconds and start reporting immediately. Within a week you will know whether you have a boiler quietly running $2,500 a month into a drain. Our ROI breakdown covers the math, and our NOI explainer covers how water savings flow straight to the bottom line.

Chart and figures are from NOWi's own monitoring data for a single multifamily property, August 2026. Building and owner withheld. Dollar figures use a combined water and sewer rate of roughly two cents per gallon.