High Water Bill in Toronto? How to Find the Hidden Leak Driving It Up
By Serhiy Marunchuk, Master Plumber · Licence T95-4969603 · Updated June 15, 2026
A sudden jump in a Toronto water bill almost always traces back to one of a few hidden leaks: a silent toilet flapper, a pinhole in a supply line, a slab leak, or a leak on the buried service pipe between the city main and your meter. The meter test confirms it in under two hours — read the meter, use no water, read again. If the dial moved, water is escaping somewhere you cannot see.
Published June 15, 2026
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Introduction
A water bill that suddenly doubles or triples is rarely a billing error — in a metered Toronto home it almost always means water is moving when no tap is open. The usual suspects are a silent toilet flapper, a pinhole leak on a copper supply line, a slab leak under the basement floor, or a leak on the buried service pipe you are responsible for. The good news is you can confirm a hidden leak yourself with the meter test in under two hours, narrow down the source, and know whether it is a $25 flapper swap or a service-line repair before anyone picks up a tool. This guide walks through the meter test, the most common causes ranked by how often they drive a bill spike, and what each fix typically involves.
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Quick answer
A high water bill on a metered Toronto property almost always means a hidden leak. Confirm it with the meter test: write down the meter reading, use no water anywhere for one to two hours, then read it again — if the numbers changed, you have a leak. The single most common cause is a silent toilet leak (a worn flapper can pass hundreds of litres a day without a sound), followed by leaking supply lines, slab leaks, and leaks on the buried service line. Toilet and fixture fixes are usually inexpensive; slab and service-line leaks need professional detection (acoustic, thermal, or tracer-gas) and a planned repair. Catching it early is the difference between a small parts swap and a mould or excavation job.
Why is my water bill suddenly so high in Toronto?
A high water bill on a metered Toronto home almost always means a hidden leak, most often a silent toilet flapper that can pass hundreds of litres a day without a sound. Confirm it with the meter test: record the reading, use no water for one to two hours, then re-read it. If the numbers changed, water is escaping.
What usually drives a Toronto bill spike
Toronto residential water is billed by volume on a meter, so a hidden leak shows up directly as litres you never used.
A silent toilet leak is the most common cause — a worn flapper or fill valve can pass hundreds of litres a day with no visible overflow and no sound.
The meter test is the standard confirmation: a leak indicator (small triangle or dial) that keeps moving with every fixture off means water is escaping.
Supply-line and slab leaks stay hidden because the water soaks into subfloor, soil, or wall cavities instead of pooling where you can see it.
A leak on the buried service line between the city main and your meter is the homeowner's responsibility and often surfaces only on the bill or as a damp spot in the yard.
Hidden leaks behind walls can start mould within 24–72 hours under typical indoor conditions (Health Canada guidance), which is why a bill spike is worth chasing down quickly.
Many Ontario home insurance policies exclude slow 'gradual' leaks — documenting the leak and repair early is the best defence against a denied claim (Insurance Bureau of Canada guidance).
Common causes ranked, and how to tell them apart
| Likely cause | Tell-tale sign | Who confirms it | Typical fix |
|---|---|---|---|
| Silent toilet leak (flapper / fill valve) | Meter moves but stops if you shut the toilet supply; faint hiss or phantom refills | DIY dye-tablet test, then plumber if it persists | Replace flapper, fill valve, or rebuild the tank — inexpensive parts job |
| Dripping fixture or supply line | Visible drip, damp under a sink, or a warm spot from a hot line | Visual check, moisture meter | Replace washer, valve, or section of supply line |
| Slab leak (under basement floor) | Warm patch on the floor, sound of running water, meter moving with everything off | Acoustic listening, thermal imaging, tracer gas | Locate and spot-repair or reroute the affected line |
| Hidden behind-wall pipe leak | Stain or bubbling paint, musty smell, no visible source | Thermal imaging, moisture meter, acoustic | Open the cavity at the located point and repair the pipe |
| Buried service-line leak | Soggy or unusually green strip in the yard, bill spike, no interior signs | Pressure test plus locate; sometimes the city assists | Excavate and repair, or trenchless replacement of the service line |
When to chase it yourself vs call a pro
Try the DIY steps first when
The meter test shows movement and shutting individual toilet supplies stops it — that points to a toilet you can often fix with a flapper or fill-valve kit. A visible drip under a sink or at a fixture is also a reasonable DIY first pass. Run the meter test, do the toilet dye-tablet check, and tighten or replace obvious worn parts.
Call us when
The meter keeps moving with every fixture and toilet shut off, there is a warm spot on the floor or a stain on a wall with no source, you hear running water with nothing on, or the yard has a soggy strip over the service line. Those are slab, behind-wall, or service-line leaks that need detection equipment — guessing means cutting drywall or digging in the wrong place.
What we bring
Acoustic listening device, thermal imaging camera, tracer-gas kit, pressure-test gauges, and a moisture meter. We use multiple methods on the same visit to pinpoint the leak before opening anything, then quote the repair scope on the spot once it is located — usually 30–90 minutes to find it.
Sources cited in this guide
- City of Toronto — Water rates and metering(municipal)
- Health Canada — Indoor mould(federal)
- Insurance Bureau of Canada — water damage(industry)
Where to go next
If the meter is still moving after you have ruled out the toilets, Water Leak Detection & Repair is where you book the visit. We locate the hidden leak with acoustic, thermal, and tracer-gas tools before opening anything, then quote the repair.
If the leak is active and causing damage right now — water spreading across a floor or pouring from a ceiling — Emergency Plumbing is the faster route, with same-day and after-hours dispatch across Toronto and the GTA.
Turn the bill spike into a real diagnosis
If the meter test confirms water moving with everything off and the toilets are not the culprit, the next step is to locate the hidden leak — not to start cutting drywall. Leak Detection & Repair is the booking page: we pinpoint it first, then quote the repair scope once we know exactly where it is.
Common questions
How do I run the water meter test to confirm a leak?
Find your water meter (usually in the basement near where the service line enters). Write down the reading, then use no water anywhere in the house — no taps, toilets, dishwasher, or laundry — for one to two hours. Read the meter again. If the numbers changed, or the small leak-indicator triangle kept spinning, water is escaping somewhere. To narrow it down, shut the supply valves to each toilet and repeat — if the movement stops, a toilet is the cause.
Can a running toilet really make my bill jump that much?
Yes. A worn flapper or a fill valve that does not seat properly can let water trickle from the tank to the bowl continuously, day and night, with no overflow and often no sound. Over a billing period that adds up to a large, unexplained increase. The dye-tablet test confirms it: put a colour tablet or a few drops of food colouring in the tank, wait 15–20 minutes without flushing, and if colour appears in the bowl the flapper is leaking.
Whose responsibility is a leak on the buried service line?
In Toronto the buried water service line from the city main to your home is generally the property owner's responsibility on the private side of the connection. A leak there often shows up only as a bill spike or a soggy, unusually green strip in the yard. It needs a pressure test and a locate to confirm, and the repair is either an excavation or a trenchless service-line replacement. We can assess it and lay out both options.
Is the work warrantied?
Yes. Every job we complete is backed by a 25-year workmanship warranty. The written terms are provided with the quote. If our work fails within 25 years of the install date, we come back and make it right.
Are you licensed in Toronto?
Yes — Master plumber T95-4969603, Plumbing contractor T94-4992639, Drain contractor T87-4722944, Building renovator T85-4728632, Plumbing license FI6216638. Tornado has been serving Toronto and the GTA since 2016 with over 1,200 completed jobs.
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