What the light and the dye actually do
The method has two parts. First, a plumber adds a small amount of fluorescent dye to the water or the system being tested. Second, they darken the room and sweep a UV lamp across the suspect area. Any place the dye escapes glows bright yellow or green, even when the leak is too small to see in normal light.
The dye does not find a leak by itself. It follows water. That is why UV detection works best when the dye can travel the same path as the leak and when the escaping fluid reaches a surface you can see and light. Think of it as a tracer, not a scanner.
Where UV detection works and where it does not
| Suspected leak | UV dye and light | Better or added method |
|---|---|---|
| Toilet tank leaking into the bowl | Works well. Dye in the tank shows color in the bowl. | None needed in most cases |
| Drain or trap seam that weeps | Works well on visible joints and under sinks | Camera if the pipe is hidden |
| Where a drain line goes | Works as a trace if the dye surfaces somewhere you can see | Camera inspection for buried lines |
| Pressurized supply pipe in a wall | Limited, because the water may never reach a lit surface | Acoustic listening, pressure test, thermal imaging |
| Slab leak under a floor | Poor fit | Acoustic and thermal methods, then access |
| Roof or window seepage | Sometimes, with the right dye | Water testing and visual inspection |
We would rather tell you that UV is the wrong tool than sell it to you. When the leak is in a pressurized pipe behind drywall, we choose from other methods and explain why. Our leak detection service covers the whole menu, so the method fits the problem.
Try these checks before anyone arrives
Run the meter test
Turn off every faucet and appliance. Look at your water meter. If the small dial or the flow indicator still moves, water is going somewhere.
Do the toilet dye test yourself
A few drops of food coloring in the tank, then wait fifteen minutes without flushing. Color in the bowl means the flapper is leaking.
Look under every sink and behind the appliances
Use a flashlight and a dry paper towel on the traps, the supply lines, and the dishwasher and washer hoses.
Check the water heater base
A damp pan, rust streaks, or a puddle suggests a fitting or the tank itself. Note it but do not touch electric connections with wet hands.
Mark the stain
If a ceiling or wall has a stain, outline it in pencil and date it. If it grows, the leak is active, and that is useful information for the plumber.
If the meter still moves after those checks and you cannot find a wet spot, the leak is likely hidden. That is the time to call, because a slow leak behind a wall can rot framing and grow mold long before the water bill shows it.
What a dye and light visit looks like
The usual order of work
- Interview. We ask where you saw water, when it appears, and whether it follows rain, laundry, or a flush. Patterns point to the source faster than tools do.
- Dry-out and baseline. We wipe the area dry and shine the lamp first, so old stains and fresh dye are not confused.
- Dye in the suspect system. The dye goes into the toilet tank, the drain, or the line we are tracing, and we wait long enough for it to travel.
- Darkened sweep. With the room dim, we scan joints, seams, and the floor around fixtures. A glow marks the exit point.
- Report and repair plan. You get a plain explanation of what we saw, what it means, and what the fix involves, with the price stated before work begins.
The dye is only a clue. A glowing joint tells us where water escapes, but the cause may sit upstream, such as a loose connection, a cracked fitting, or pressure that is too high. The repair should address that cause, not only the visible drip.
When a leak becomes an emergency
A drip under a sink is a repair. Water spraying from a pipe, a ceiling that is sagging, or a wet floor near electrical outlets is an emergency. Close the main shutoff, usually near the water meter or where the line enters the house, and call. Our burst pipe repair team works around the clock for this.
Once the flow is stopped, UV dye and other tools can help find the original failure point so the repair is complete. A quick patch without a diagnosis tends to come back at the next weak joint.
Lake Forest and Gurnee: where water goes after a storm
What Lake Forest and Gurnee say about sump pumps, sewer connections, and flooding
Lake Forest requires a Home Sewer Inspection when water billing is transferred on the sale of a single-family home or duplex. The inspection checks downspouts, sump pumps, and yard drains for unauthorized connections to the sanitary sewer. The city lists a fee for the inspection and one for a re-inspection, and it says permits are needed before correction work.
The Lake County Stormwater Management Commission reports that the July 2017 storm put about four inches of rain on Lake Forest in four hours at its peak.
Gurnee's village page says that a gravity sewer backup or a sump pump failure will likely lead to basement flooding, and it encourages residents to install backup systems. The village names the low-lying area around the Des Plaines River and its tributaries as its most dangerous flood hazard area.
A burst of rain like that is when a downspout or sump line tied to the wrong pipe shows itself.
For a home in the city, a dye trace can show where a questionable drain line ends before the inspector arrives, and a wet basement after a storm can be sorted into groundwater seepage or a plumbing leak by testing the plumbing side. See our Lake Forest plumber page for the area, and our Gurnee plumber page for the village, both a short drive from our Skokie Highway address.
Call us if the water keeps showing up and you cannot see why. We will pick the method that fits.
Call (847) 281-8626UV light and leak questions
Leak-detection dyes are made for plumbing and are used in small amounts. Ask what product we plan to use and read its safety sheet if you want to. For drinking water lines, we rely on other methods instead of adding dye.
Rarely. The dye has to travel with the leaking water to a place the lamp can see. A sealed wall blocks that. For pressurized lines inside walls we use listening gear, pressure testing, or thermal imaging, and open the wall only where the evidence points.
The principle is the same. Food coloring in the tank shows a flapper leak with no tools. A plumber's UV kit uses a dye that glows, so a much smaller amount shows up even in a hard-to-see spot.
It can help you find out where a suspect downspout, sump line, or yard drain connects, so you can correct it before the inspection. It does not replace the city's inspection or its permit steps. Ask the city about scheduling and fees.
Yes. Leaks do not keep office hours, so we are open 24/7. Shut off the water, turn off power to any wet area if you can reach the breaker safely, and call.
Find the leak before it finds your floor
Call and describe what you have seen. We will recommend a method and give a clear price before work starts.
Call (847) 281-8626