Water is the utility most buildings measure least and waste most. A leaking flush valve runs continuously and silently, and on a quarterly municipal bill it is invisible until the bill arrives with an extra few thousand dollars on it. Water submetering is how buildings see that sooner, and how they allocate a shared bill to the tenants who actually caused it.
It is worth saying at the outset that water submetering is not electricity submetering with a different unit. The regulation is different, the data is coarser, and the problems it finds are a different class of problem.
How the regulation differs
Electricity and gas meters used for billing in Canada fall under a single federal statute. The Electricity and Gas Inspection Act requires, in section 9(1), that a meter used "for the purpose of obtaining the basis of a charge" be verified and sealed before it goes into service, and section 9(4) requires the meter's class, type or design to be approved.
Water is not in that Act. Water service is municipal, and the rules about metering, billing and who may resell it are set locally and provincially rather than federally. Measurement Canada administers the federal regime for electricity and gas, and water simply is not within it. That has two practical consequences.
- The hardware specification is driven by the municipality's own requirements and by your insurer, not by a single national approval regime.
- Whether you may bill a tenant for water at all, and on what basis, is a question about your lease and your local by-laws. Some jurisdictions restrict reselling water above cost.
- The meter you install for information purposes is unregulated, which makes an information-only deployment much cheaper to specify than the electricity equivalent.
Check the by-law before you specify anything. Municipal water departments publish their metering requirements, and they vary more than people expect between neighbouring cities.
What water submeter data looks like
A water submeter counts volume, usually in cubic metres, sometimes in gallons on older equipment. A pulse output or a register read gives you a cumulative total, and the interval series is derived by differencing consecutive reads.
The resolution is the thing to watch. A meter whose smallest counted increment is a tenth of a cubic metre will show nothing at all on a slow leak until hours have passed. The same meter read once a quarter by a person with a clipboard produces four numbers a year, which is enough to bill from and useless for finding a problem.
| Read frequency | What you can do with it | What you cannot see |
|---|---|---|
| Quarterly manual | Allocate the bill | Anything that started after the last read |
| Monthly | Compare against last year, spot a step change | Which day or which hour it started |
| Daily | See a leak within days, separate weekday from weekend | Short high-flow events |
| Hourly or finer | Separate overnight base flow from occupied use, catch a continuous leak immediately | Very little that matters at building scale |
The single most valuable derived figure is overnight minimum flow. In a building that should be empty at three in the morning, any sustained flow is either a leak, a cooling tower, or an irrigation controller nobody told you about. It is a simple query against hourly data and it pays for the metering.
Where water submetering pays for itself
Continuous leaks
A flush valve stuck partly open, a chilled water make-up line, an irrigation zone with a failed solenoid. All three run indefinitely at a rate too small to notice and too large to ignore over a quarter. Hourly water data turns each of them into a same-week discovery rather than a bill-day surprise.
Cooling tower make-up and blowdown
Towers consume a lot of water and their consumption is weather-driven, which means a normal summer month looks like a leak and a leaking tower looks like a normal summer month. Submetering the tower separately from domestic supply is what lets you tell the two apart, and it is also what makes a sewer credit application possible in municipalities that offer one, since water evaporated in a tower never reaches the sewer.
Tenant allocation in mixed-use buildings
A restaurant, a gym and an office in one building have wildly different water intensity per square foot. Allocating by area is not a rough approximation in that situation, it is a transfer of cost from the heavy user to everyone else.
Irrigation
Irrigation is the load most likely to be running on a schedule nobody has reviewed since the landscaping was installed. Metering it separately makes the schedule visible and, again, may qualify for a sewer credit.
The data handling that makes it work
Water data has one quirk that catches people: the meter is cumulative and the interval series is a derivative of it. That means every gap in the read series turns into a spike in the derived consumption, because the volume that accumulated during the gap all lands in the first read after it.
- Keep the raw cumulative register reads, not only the derived intervals. A derived series cannot be repaired; a register series can be re-differenced.
- Handle register rollover explicitly. A five-digit register that passes 99999 and returns to zero produces a large negative interval unless the processing knows the register size.
- Flag gaps rather than interpolating silently. An interpolated value that later gets billed as real consumption is a figure you cannot defend.
- Reconcile the submeters against the municipal bill every period. The difference is house load, unmetered branches, or a meter that stopped, and you want to know which.
The same discipline applies to any commodity read from a cumulative register, which is why we treat gas, water and propane the same way as electricity in natural gas, water and propane data alongside electricity.
How it fits with the rest of your utility data
Water is usually the last commodity a building instruments and the first one that produces an obvious saving, which makes it a good place to start if you are building the habit. But it only produces that saving if somebody looks at it on a schedule, and that is a data pipeline question rather than a hardware question.
The practical arrangement that works: municipal water bills give you the billed truth and the cost, submeters give you the distribution and the timing, and the two get reconciled every period so that a divergence is noticed. Building owners who do only the first have accurate costs and no ability to act on them. Those who do only the second have interesting charts and no idea whether they match the invoice.
For the whole-building record, see collecting utility data across a property portfolio. For the electricity side of submetering, which is regulated quite differently, see electricity submetering and the data it produces.
Benchmarking programs treat water as a separate metric from energy, and water use intensity is reported alongside energy use intensity in ENERGY STAR Portfolio Manager, so a building working towards a benchmark score needs the water record to be as complete as the energy one.
A short checklist before you install
- Confirm what your municipal by-law and your lease allow you to bill, and on what basis.
- Decide whether this deployment is for billing or for information, and specify accordingly.
- Pick a read frequency based on the smallest problem you want to catch. Daily is the minimum for leak detection; hourly is better.
- Meter the cooling tower and irrigation separately from domestic supply. These are the two loads where separation changes decisions.
- Require raw register reads in the data export, not only derived consumption.
- Put the overnight minimum flow check on a schedule from day one. It is the report that finds the money.
Frequently asked questions
Are water submeters regulated like electricity meters in Canada?
No. Electricity and gas meters used for billing fall under the federal Electricity and Gas Inspection Act. Water is a municipal service, so metering and billing requirements are set locally and provincially. Check the municipal by-law and your lease before billing tenants for water.
How often should water submeters be read?
Daily is the minimum if you want to catch leaks, and hourly is better. Quarterly manual reads are enough to allocate a bill and useless for finding a problem, because anything that started after the last read is invisible until the next one.
What is overnight minimum flow and why does it matter?
It is the lowest sustained flow rate during hours when the building should be empty. In a building with no legitimate overnight water use, any sustained flow is a leak, a cooling tower, or an irrigation controller. It is the single most valuable number water submetering produces.
Should the cooling tower be metered separately?
Yes, for two reasons. Tower consumption is weather-driven, so mixing it with domestic supply makes both harder to interpret. And in municipalities that offer a sewer credit for evaporated water, a separate tower meter is usually what the application requires.
Why does our derived water consumption show impossible spikes?
Almost always a gap in the read series or a register rollover. Water meters are cumulative, so consumption is derived by subtracting consecutive reads. A missing read makes the next interval absorb everything that accumulated during the gap, and a register passing its maximum and returning to zero produces a large negative value unless the processing knows the register size.