Water Meters, Sub-Metering And Leak Detection

The most expensive leaks in a building are the ones that never appear as a stain on a ceiling.

Underground pipework, a running toilet in an empty apartment, an irrigation line, a leaking sump. They cost money every day and they produce no symptom other than a water bill nobody looks at closely.

The overnight test

The simplest diagnostic available and almost nobody uses it.

Read the main meter late at night when the building should be using nothing. Read it again early in the morning.

If the reading has moved, the building has a leak or something is running. If it has not, the meter is telling you the distribution is sound.

Five minutes, no equipment, and it turns a suspicion into a fact.

Where the water actually goes

Toilets. A silently running cistern is the single most common continuous loss in residential buildings. The flush valve seal fails, water runs from the cistern into the pan continuously, and it makes no noise. In a vacant or a rented apartment it can run for months.

The test is a few drops of food colouring in the cistern. If colour appears in the pan without flushing, it is leaking.

Irrigation. Systems on a timer with a cracked line or a failed solenoid, running into the ground.

Underground mains. Between the meter and the building. This is the one that produces no symptom at all until the ground is saturated or the bill arrives.

Fire services. Leaking valves or a failed test point on a fire system, which is on its own supply and rarely checked.

Hot water systems. A leaking pressure relief valve discharges continuously to a drain, and because the discharge is to a drain nobody sees it.

Cooling towers and plant in larger buildings.

Sub-metering

In many buildings, water is a common cost split across owners rather than metered per apartment.

That means an owner with a running toilet pays a small share of their own waste, so there is no reason for them to fix it. Sub-metering changes that, and consumption typically drops when people see their own use.

It also makes leak detection far easier, because a single apartment with abnormal consumption is immediately visible rather than hidden inside a building total.

Retrofitting sub-meters depends on how the building was plumbed. Where each apartment has a single supply point, it is straightforward. Where the plumbing was run as a shared loop, it may not be practical without significant work.

Establishing which situation the building is in is the first question and it is answerable from the riser.

Monitoring rather than reading

Smart meters and simple flow monitors on the main supply can alert on continuous flow, which is the signature of a leak.

The value is speed. A leak found in a day instead of a quarter is a different cost entirely, and for a building with a history of water bills that move around, it pays for itself quickly.

Leak detection when the meter says there is one

Once the overnight test proves a leak, finding it is a specialist process.

Isolating sections of the building to narrow it down. Acoustic detection for pressurised lines. Thermal imaging for hot water lines. Pressure testing individual sections.

The isolation step is often enough on its own, and it is the cheapest, so it comes first.

What a building manager should do

Read the main meter monthly and record it. A trend is far more useful than a single reading, and a step change is the signal.

Run the overnight test quarterly, or immediately if a bill jumps.

Dye-test the toilets in vacant apartments as part of the turnover check. This one habit removes the most common continuous loss in the building.

Check the hot water relief valve discharges when servicing.

We carry out meter testing, leak detection, sub-meter installation and the repairs under plumbing. If your water bills have moved and nobody can say why, start with the overnight test.