When we switched on water monitoring across a Los Angeles apartment portfolio of 47 buildings and 1,789 units, almost three out of four buildings were already leaking. The owners had no idea. The leaks were not dramatic floods. They were quiet, continuous flows running behind the meter, day and night, showing up only as a slightly higher water bill nobody had time to question.
This is what the first week of data looked like, and why it matters for anyone who owns or manages apartments.
The short version
Each building got a single strap-on water monitor on its main line. No plumbing cuts, no shutoff, no electrician. Within seven days of each device going live, the data showed:
in wasted water uncovered across the portfolio in the first week of monitoring.
Dollar figures use the Los Angeles LADWP multi-unit residential water rate plus sewer, which together run to roughly two cents per gallon in 2026. At that price, small leaks add up fast.
Hidden leaks are the norm, not the exception
The most common reaction to this data is disbelief. Surely most buildings are fine? They are not. The EPA estimates the average household wastes about 10,000 gallons a year to leaks, and roughly 14% of all residential water use is lost to leaks. Multiply that across dozens of units per building and the leaks become continuous, not occasional.
In this portfolio, leaking water made up 8.5% of everything metered in the first week. In the worst building, nearly half of all the water it used was going straight to a leak. Most of these are the unglamorous kind: running toilets and open flappers, a stuck irrigation valve, a slab leak under a courtyard. None of them trip an alarm. They just run.
The problem is not that owners are careless. It is that a monthly water bill cannot tell you a toilet has been running since the 3rd. By the time the bill arrives, the water is long gone, and the bill blends one leak into the noise of normal use. Continuous, minute-by-minute data is the only way to separate a leak from a busy laundry day.
A few buildings were leaking a lot
Leaks are not spread evenly. Most buildings had a small leak or none. A handful were hemorrhaging water. The single worst case was a 171-unit building losing about 7,351 gallons a day, roughly $4,400 a month, all of it running continuously behind the meter until the data flagged it.
Largest leak found at each building, by monthly cost
For an owner, this is the useful part. You do not have to inspect 47 buildings. The data ranks them for you, so the maintenance team goes straight to the seven buildings bleeding real money.
What monitoring actually costs you
Less than you would guess. There is no construction. A maintenance tech straps the device to the existing pipe or meter in seconds, it runs on a multi-year battery, and it reports over cellular, so there is no WiFi or building IT to involve. The whole system for a building costs a fraction of one month's water bill, and it starts paying for itself the moment it finds the first leak.
The ROI is not just the water bill
Recovered water is the obvious win, but it is not the biggest one.
Repair certainty
Without monitoring, a maintenance team fixes a toilet and then waits 30 to 60 days for the next water bill to find out if it worked. With real-time data, they see the flow drop the moment the repair succeeds. No repeat truck rolls, no guessing. The fix either shows up in the data or it does not.
Root cause from timestamps
When you know exactly when unusual usage started, the cause is often obvious. A spike every night at 2 AM is an irrigation valve, not tenants. A steady flow that never stops is a running toilet or a buried irrigation leak, not showers. The timestamp does half the diagnosis.
Avoided water damage
A running toilet wastes money. A failed supply line floods a unit. The average water damage claim runs $13,954, and that is before rising deductibles and displaced tenants. Catching an abnormal flow early is the difference between a maintenance ticket and an insurance claim. It also puts you in a stronger position with your carrier, though premium reductions are never guaranteed.
The numbers from this portfolio
No hypotheticals. This is what leaks were actually costing across the 47 buildings, in wasted water alone, at the local LADWP water and sewer rate:
| Measured leak cost | Per year |
|---|---|
| Average leaking building | ~$5,600 |
| Worst single building | over $50,000 |
| Per apartment unit | ~$106 |
| Across the whole portfolio | ~$190,000 |
| Typical monitoring cost, year one | A fraction of one month's water bill |
Recovering even the measured 8.5% that was leaking pays back the monitoring in weeks, which lines up with what we have seen in other deployments and with the broader picture that most hidden leaks go unnoticed until they are expensive. And that is before the avoided-damage upside above.
Getting started is low risk
You do not have to wire up a whole portfolio to find out if this applies to you. Start with a handful of buildings, or the ones with water bills that never quite make sense. The devices go on in seconds and start reporting immediately. Within a week you will know exactly where your water is going, the same way this LA portfolio did. If you want the deeper background, our ROI breakdown and low-rise apartment case study go further, and our NOI explainer covers how water savings flow straight to the bottom line.
Ready to see what water waste is costing your buildings?
Request a Free Water Assessment →Figures are from NOWi's own leak detection over each device's first seven days after installation across a 47-building Los Angeles multifamily portfolio, 1,789 units total. Building addresses withheld. Water cost based on the LADWP combined water and sewer rate.