ARC Plumbing · Toilet leak test
Got a blue tablet from us? Here's the 30-minute toilet test.
A toilet can leak without a sound and without a drop on the floor: water slips from the tank into the bowl and straight down the drain, all day. The tablet shows you whether yours is doing it. Takes one minute of effort and half an hour of waiting.
Wake County utilities bill for every gallon that goes through the meter, leak or not. Further down: what a leaking toilet costs here, and what it does if you're on a well.
The test
Six steps. Nothing to unscrew.
- 1
Flush the toilet once
Let it finish refilling. You want a full, settled tank before the tablet goes in.
- 2
Lift the lid off the tank
The tank is the box behind the seat. The lid is heavy ceramic; set it flat on the floor, not on the seat.
- 3
Drop in one tablet
One tablet in the tank water. It fizzes and turns the water blue in a minute or two. Don't touch it with wet fingers.
- 4
Put the lid back
And walk away. Nothing else to do.
- 5
Wait 30 minutes to an hour
Don't flush. Don't use that toilet. Go make dinner.
- 6
Look in the bowl
Clear water: no leak. Any blue in the bowl, even a faint tint: water is getting past the flapper or fill valve without a flush. That's the leak.
No tablet? A few drops of food coloring in the tank does the same thing; the EPA suggests checking after 10 minutes.1 Either way, flush a couple of times when you're done so the dye doesn't sit in the bowl.
What you'll see
Clear bowl or blue bowl
Clear: no leak
The flapper is sealing and the fill valve is shutting off. Flush a couple of times to clear the dye from the tank. Test again in a year; rubber parts wear.
Blue in the bowl: it's leaking
Water is getting from the tank to the bowl without a flush. Almost always it's the flapper, a rubber seal at the bottom of the tank that has hardened or warped. Sometimes it's the fill valve letting water run over the overflow tube. Either way the meter is turning while you sleep. Slow leaks can be imperceptible: no sound, no ripple, nothing on the floor. Some are intermittent, running for a stretch after a flush and then sealing again for a while, which is why the test waits a full half hour and why a faint tint still counts.
Toilets are the biggest water user inside most homes, about 30 percent of indoor use, and the EPA says most toilet leaks come down to that old flapper.2 The Town of Cary puts it simply: 1 in 4 toilets leaks.3
On city water
What a leaking toilet costs in Wake County
A leak you can't hear can still move a lot of water. The EPA says nine percent of homes have leaks wasting 50 gallons or more a day, and a toilet that runs constantly can waste more than 200 gallons a day.1,4 Raleigh Water bills water in CCFs (1 CCF = 748 gallons) and bills sewer on the same gallons, so a leak is paid for twice.5,6 At Raleigh's inside-city rates, that works out to:
| Leak | Water wasted | Added to your bill |
|---|---|---|
| Slow, silent flapper leak (about 50 gal/day) | about 1,500 gallons a month, 2 CCF | about $21 a month, $250 a year |
| Toilet that runs constantly (200+ gal/day) | about 6,000 gallons a month, 8 CCF | about $84 a month, $1,000 a year |
Assumes your usage is already in Raleigh's 5–20 CCF tier, which most households are. Outside city limits the rates are double. Garner, Knightdale, Rolesville, Wake Forest, Wendell and Zebulon are on Raleigh's system; Cary, Apex, Holly Springs and Fuquay-Varina bill on their own rate schedules; check your town's. If a leak did run up a Raleigh bill, Raleigh Water allows one leak adjustment per twelve months with a plumber's receipt or other proof of repair.7
On a well
No water bill, but the leak still costs you
Your pump pays for every gallon
On a well, every gallon a leaking toilet sends down the drain is a gallon the pump had to lift out of the ground. A running toilet means the pump runs for it, around the clock, and that shows up on the power bill instead of a water bill.
A small leak is worse for the pump than a big one
A slow leak bleeds pressure out of the tank a little at a time, so the pump kicks on for a short burst, shuts off, and does it again all night. The EPA-funded Private Well Class notes that frequent cycling "both wastes energy and is hard on the pump."8 Franklin Electric, one of the largest makers of submersible well motors, says excessive cycling "reduces the life of control components such as pressure switches, starters, relays, and capacitors" and "can also cause motor spline damage, bearing damage, and motor overheating."9 A flapper costs a few dollars. A well pump doesn't.
Quick check for well owners: with nothing running in the house, stand near the pressure tank for ten minutes. If the pump clicks on by itself, something is leaking, and a toilet is the first place to look. We don't repair well pumps, but we'll find and fix the leak that's wearing yours out.
Sources
Where these numbers come from
- U.S. Environmental Protection Agency, WaterSense. Fix a Leak Week: "nine percent of homes have leaks that waste 50 gallons or more per day"; the food-coloring test.
- U.S. EPA, WaterSense. Residential Toilets: toilets are "nearly 30 percent of an average home's indoor water consumption"; "Most toilet leaks are due to old or worn-out toilet flappers."
- Town of Cary. Fix a Leak: "1 in 4 toilets leaks."
- U.S. EPA, WaterSense. Fix a Leak Week student worksheet (PDF): "A constantly running toilet can waste more than 200 gallons of water every day."
- City of Raleigh, Raleigh Water. Water and sewer rates effective July 1, 2025 (PDF): residential water 5–20 CCF $5.23, sewer $5.13 per CCF, inside city limits.
- City of Raleigh, Raleigh Water. Utility Rates, Deposits & Other Charges: "1 CCF = 748 gallons."
- City of Raleigh, Raleigh Water. Leak Adjustment: one adjustment per twelve months with proof of repair.
- Private Well Class (Rural Community Assistance Partnership and the University of Illinois, funded by the U.S. EPA). How does my private well pressure tank work?
- Franklin Electric. Submersible Motors Application, Installation, Maintenance Manual (PDF), "Frequency of Starts."
Blue bowl? Here's the honest answer
Most of the time it's a flapper. Some of the time it isn't.
If you're handy
A flapper is a cheap rubber part and the EPA calls replacing one "quick and easy."2 Shut the supply valve under the tank, flush to empty it, unhook the old flapper from the two pegs and the chain, hook on the new one, turn the water back on. Take the old one to the hardware store so you match the size. Then run this test again.
When to call us
You replaced the flapper and the bowl still turns blue. The fill valve won't shut off. The tank bolts are weeping, the toilet rocks, or it's older than the house's last owner. Those are the calls where a new fill valve, a reset, or a new toilet is the right fix, and we'll tell you which before any work starts.
Free in-home quotes Mon–Fri 8–5. Price in writing before we touch anything. Our plumbers aren't paid on what you spend. More on toilet repair and replacement.
Questions
About the test
Will the blue dye stain my toilet?
Not if you flush it through within a few hours. It's the same food-grade dye water utilities hand out for this test. Don't leave it sitting in the tank for days.
The bowl turned a little blue. Does a small leak matter?
Yes. A leak you can't hear or see is still 24 hours a day. At Raleigh Water's rates a slow flapper leak adds roughly $20 a month between water and sewer, and small leaks get bigger as the rubber keeps wearing.
Can I use food coloring instead of the tablet?
Yes. A few drops of dark food coloring in the tank does the same job. The EPA says to check the bowl after 10 minutes; our tablets are stronger, so 30 minutes to an hour gives a clearer answer.
My toilet makes a refill sound every so often but passed the test. What is that?
That's usually the fill valve topping off because the flapper let a little water past, or a fill valve that doesn't fully seat. Run the test again and wait the full hour. If it still passes, the sound is worth a look during a regular visit, not an emergency.
Where do I get more tablets?
Ask any ARC plumber on a visit, or pick them up at an event where we have a table. Until then, food coloring works.
2406 Waco Commercial Ct
Fuquay-Varina, NC 27526
(919) 888-3500
NC Plumbing Contractor License #36473 · Serving Raleigh and all of Wake County · The ARC Promise