Does a thermal camera see through walls and floors?

No, and this is the single most common misunderstanding about it. It measures the temperature of the surface it is pointed at. If something behind that surface has changed its temperature, the pattern shows up. If it has not, there is nothing to see, no matter what is behind it.

Not directly. Evaporating water cools a surface, so damp often appears as a cool patch, but what is being measured is temperature and not moisture. A cool patch can be damp, or a draught, a cold bridge, a shadow or a different material. Damp meters measure moisture; thermal cameras do not.

When is it the right method?

When the water is at a different temperature from its surroundings and the surface is one the camera can see. A hot water pipe or a heating circuit under a floor is the ideal case, because it warms a stripe of floor a camera picks up immediately. A cold supply pipe under a cold slab is the opposite.

Why does it show things that are not leaks?

Because plenty of ordinary things change a surface temperature. Pipe runs that are working normally, underfloor heating, a cold bridge at a wall junction, a draught under a door, sunlight through a window an hour ago, and a patch of a different material all produce a pattern. The camera reports all of them equally, and the interpretation is the skilled part.

Can I do this with a phone attachment?

You can produce an image. Interpreting it is the difficulty, and this is the method where a wrong interpretation is most convincing, because you have a picture. If you do try, take the same view again on a different day and at a different time; a pattern that moves with the sun or the heating schedule was never a leak.

What thermal imaging can and cannot show

A thermal camera measures the temperature of surfaces. It does not see water, it does not see through floors or walls, and it does not detect moisture. A leak shows up only when the escaping water has made a surface the camera can look at warmer or cooler than the surface around it. That makes it excellent for hot water under a floor and close to useless for cold water in a cold slab, and it makes everything it finds a lead that needs confirming by something else rather than a position you can dig on.

Last reviewed 14 August 2026

The short answer

It shows the temperature of surfaces. Everything it can and cannot do follows from that one sentence.

A leak becomes visible when it has changed the temperature of something the camera can look at. Hot water under a floor does that quickly and obviously. Cold water in an already cold floor may not do it at all. The camera is not failing in the second case, there is simply nothing there for it to measure.

How this works in practice

Every surface gives off infrared radiation according to how warm it is, and the camera turns that into a picture where colour means temperature. Water changes surface temperature in two opposite ways.

Hot water warms what it soaks into, so a hot pipe or heating circuit leaking under a floor shows as a warm patch or a stripe following the pipe run.
Cold water, and water evaporating from a surface, cools it, so a cold supply leak can show as a cool patch, provided there was a temperature difference to start with.

The first of those is far more reliable than the second, because the temperature difference is larger and it is being created continuously by the water rather than by evaporation. This is why thermal imaging is at its best on heating and hot water faults and at its weakest on cold supply pipes.

A useful trick that follows from the mechanism rather than from the equipment: if you can change the temperature of the water deliberately, you can make a leak appear. Running the hot water or the heating for a while before looking gives the camera something to see that was not there before, which is a manufactured temperature difference rather than a lucky one.

What changes the answer

This method fails differently from the other two, and the difference matters. Acoustic and tracer gas mostly fail by finding nothing. Thermal imaging fails by finding something.

Failure	What happens	Why it is a problem
No temperature difference	Cold water in a cold floor produces nothing to see.	A clean-looking survey that establishes nothing. The absence of a pattern is not the absence of a leak.
A covering the camera cannot see through	Thick screed, insulation, carpet, or a void between the pipe and the surface.	Same result, for a different reason. The heat never reaches a surface the camera can look at.
Something that is not a leak	Pipe runs working normally, underfloor heating, a cold bridge, a draught, sunlight earlier in the day, a different floor material.	A confident-looking image of something that was never a leak. This is the distinctive risk of the method.

Where thermal imaging goes wrong

The third row is why a thermal image should be treated as a lead rather than a result. A picture is persuasive in a way that silence is not, so a false positive here is more likely to be acted on than a false negative from a method that simply heard nothing. Before anything is lifted on the strength of a thermal image, it is fair to ask what else confirms it.

Which is why it is worth asking what confirms a thermal result rather than acting on the image alone. how a suspected position is confirmed by listening is the usual second opinion where the pipe is under pressure.

Assumptions and sources

Drip Calculator: how much water does a leaking faucet waste?

United States Geological Survey, Water Science School · primary source

Faucet drip volume, adopted: 0.25 ml
Faucet drip volume, measured range: 0.2 to 0.33 ml
Bath tap drip volume: 0.5 ml
Drips per US gallon: 15140 drips
Drips per litre: 4000 drips

The pharmacopoeial metric drop, 20 drops to 1 millilitre

United States Pharmacopeia, British Pharmacopoeia and European Pharmacopoeia convention · primary-standard source

Standard drop volume: 0.05 ml

Tate's law: the weight of a falling drop

Thomas Tate, Philosophical Magazine, 1864, with the later drop-weight literature · primary source

Drop weight: W = 2 * pi * r * gamma equation

Plumbers shine the spotlight on dripping taps during Water Saving Week

WaterSafe, with Waterwise · untraceable source

Claimed annual waste from a dripping tap: 5500 litres per year

OIML R 49-1, Water meters for cold potable water and hot water, Part 1: Metrological and technical requirements

International Organization of Legal Metrology · primary-standard source

MPE, accuracy class 2, lower zone Q1 to Q2: 5 %
MPE, accuracy class 2, upper zone Q2 to Q4: 2 %
MPE, accuracy class 1, lower zone: 3 %
MPE, accuracy class 1, upper zone: 1 %
In-service MPE multiplier: 2 ratio
Q2 / Q1: 1.6 ratio
Q4 / Q3: 1.25 ratio

Aquadis+ DN15 and DN20 specification sheet

Itron · manufacturer source

Q1 minimum flow rate, DN15, Q3 2.5, R160: 15.6 l/h
Q2 transitional flow rate, DN15, Q3 2.5, R160: 25 l/h
Q3 permanent flow rate, DN15: 2500 l/h
Typical starting flow rate, DN15: 0.4 l/h
Typical starting flow rate, DN20: 2 l/h
Q1 minimum flow rate, DN20, Q3 4.0, R160: 25 l/h
Flow rate at which accuracy is within +/- 5%, DN15: 3 l/h
Flow rate at which accuracy is within +/- 2%, DN15: 5 l/h
Minimum scale interval, DN15 and DN20: 0.02 l

Water resources 2024 to 2025: analysis of the water industry's annual water resources performance

Environment Agency · primary source

Household per capita consumption: 136.5 l/person/day
Household per capita consumption, prior year: 137 l/person/day
Household per capita consumption, dry-year adjusted: 140.3 l/person/day
National leakage: 2617 Ml/day
National leakage as share of water put into supply: 19 %

PR24 common performance commitments: per capita consumption (PCC), version 2.1

Ofwat · primary-standard source

PCC formula: (measured household consumption + unmeasured household consumption) / total household population l/person/day

Leaky loos, why it's not as simple as faulty flush valves

ech2o, reporting research attributed to Thames Water · secondary source

Toilets inspected: 58551 toilets
Toilets found leaking: 4854 toilets
Prevalence: 8.3 %
Average residential leak rate: 400 l/day
Average commercial leak rate: 2100 l/day
UK-wide average across all WCs, leaking and sound: 20 l/day
Share of leaking toilets with flush valves rather than siphons: 81 %

Leaky Loo Position Statement

Waterwise · untraceable source

Single leaking toilet: 215 to 400 l/day
Share of toilets leaking: 5 to 8 %
UK total from leaking toilets: 400000000 l/day

Methods for Calculation of Evaporation from Swimming Pools and Other Water Surfaces

M. M. Shah, ASHRAE Transactions SE-14-001 · primary source

Outdoor unoccupied pool evaporation: E0 = (C1 + C2 * u) * (pw - pa) / ifg kg/(m2*h)
C1, SI: 235 constant
C2, SI: 206 constant

Location-specific long-term averages, Wisley, Surrey

Met Office · primary source

Annual mean daily maximum temperature: 15.41 degrees C
Annual mean daily minimum temperature: 6.66 degrees C
Annual rainfall: 667.92 mm
Annual mean wind speed at 10 m: 5.06 knots

Annual bill

Discover Water, the water industry transparency site run with Water UK, Ofwat, CCW, the Drinking Water Inspectorate and Defra · primary source

Average annual household bill, combined water and sewerage: 639 GBP
Average annual household bill, water only: 309 GBP
Average annual household bill, sewerage only: 330 GBP

SI Brochure: The International System of Units (SI), 9th edition (2019), version 4.01, June 2026

Bureau International des Poids et Mesures · primary-standard source

cubic metre: coherent derived unit of the SI, Table 5 m3
litre: non-SI unit, Table 8. 1 l = 1 L = 1 dm3 = 10^-3 m3 l or L
bar: non-SI unit, Table 8. 1 bar = 0.1 MPa = 10^5 Pa bar

Authority URLs for the named entities in content/entities.ts

Various, see per-entity notes · primary source

WC flush volume: three UK instruments, not one

UK Statutory Instruments, Northern Ireland Statutory Rules, and Scottish Water · primary-standard source

Maximum single flush, all three jurisdictions: 6 litres
Dual flush, lesser flush maximum: two-thirds of the largest flush volume ratio
England and Wales transitional maximum, 1 Jul 1999 to 1 Jan 2001: 7.5 litres

Per-event central heating top-up volume, derived

Derived by Q3 from Boyle's law and typical UK domestic expansion vessel specifications · derived source

Water held in an expansion vessel: V_water = V * (1 - P0 / P), pressures absolute equation
Typical top-up, 8 l vessel at 1.0 bar pre-charge, 0.5 to 1.5 bar: 1.6 litres
Typical top-up, 8 l vessel at 0.75 bar pre-charge, 0.5 to 1.5 bar: 2.4 litres
Typical top-up, 12 l vessel at 1.0 bar pre-charge, 0.8 to 1.5 bar: 2.4 litres
Typical top-up, 8 l vessel at 1.0 bar pre-charge, 1.2 to 1.5 bar: 0.9 litres
Realistic range: 0.9 to 2.5 litres

Monodispersed Bubble Generation Using Hydrophobic Orifices: The Extended Tate’s Law

Bo Liu, Hao Zhang and co-authors, ACS Omega 2024, 9(17), 18854 to 18861 · primary source

No sensitivity figure, temperature threshold or accuracy claim appears here, because no sourced measurement of any of them was found. What the page states is what the instrument measures and what follows from that, which is physics rather than performance.

The distinction the page rests on is not a caveat, it is what the device is. A thermal camera is a surface thermometer that produces a picture. Everything written above about where it works and where it does not is that fact applied to different situations, and nothing about it is contested.

What is not claimed: how often thermal imaging finds a leak, how often it produces a false positive, or how it compares with the other two methods in practice. All three would need somebody to have checked a set of results against what was actually dug up, and no such work was found published.

What to do next

Three things, and the first two decide whether the method has anything to work with.

Work out whether the water in the suspect pipe is hot or cold. Hot is the case this method is good at. Cold in a cold floor is the case it is worst at, and that is worth establishing before rather than after.
Note what is over the pipe. Tile or vinyl on screed gives the camera a surface to read. Thick insulation, a deep void or a carpet does not.
If you look yourself, look twice, at different times of day and with the heating in different states. A pattern that follows the sun or the heating schedule is telling you about the sun or the heating.

What thermal imaging establishes, at its best, is that a surface is warmer or cooler in a particular place. What it leaves unknown is why. Every one of the ordinary explanations has to be ruled out before the pattern means water, and the camera cannot do that part.

Common questions

Does a thermal camera see through walls and floors?: No, and this is the single most common misunderstanding about it. It measures the temperature of the surface it is pointed at. If something behind that surface has changed its temperature, the pattern shows up. If it has not, there is nothing to see, no matter what is behind it.
Does it detect damp?: Not directly. Evaporating water cools a surface, so damp often appears as a cool patch, but what is being measured is temperature and not moisture. A cool patch can be damp, or a draught, a cold bridge, a shadow or a different material. Damp meters measure moisture; thermal cameras do not.
When is it the right method?: When the water is at a different temperature from its surroundings and the surface is one the camera can see. A hot water pipe or a heating circuit under a floor is the ideal case, because it warms a stripe of floor a camera picks up immediately. A cold supply pipe under a cold slab is the opposite.
Why does it show things that are not leaks?: Because plenty of ordinary things change a surface temperature. Pipe runs that are working normally, underfloor heating, a cold bridge at a wall junction, a draught under a door, sunlight through a window an hour ago, and a patch of a different material all produce a pattern. The camera reports all of them equally, and the interpretation is the skilled part.
Can I do this with a phone attachment?: You can produce an image. Interpreting it is the difficulty, and this is the method where a wrong interpretation is most convincing, because you have a picture. If you do try, take the same view again on a different day and at a different time; a pattern that moves with the sun or the heating schedule was never a leak.