Most running toilets come down to one of three parts: a worn flapper (the rubber seal at the bottom of the tank), a float set so high that water spills into the overflow tube, or a fill valve that no longer shuts off. Replacing a flapper takes about ten minutes and an inexpensive part. Before you buy anything, do the dye test: put a few drops of food coloring in the tank, wait ten minutes without flushing, and look in the bowl. Color in the bowl means the flapper is leaking. No color, but the toilet still runs, and the problem is the fill valve or the float instead. That single test tells you which of the repairs below you actually need.
It is worth doing today rather than on the weekend. Denver Water puts the average leaking toilet at about 200 gallons (757 liters) a day, which it estimates adds $270 to $470 a year to a Denver customer’s bill. EPA WaterSense estimates that household leaks of all kinds waste nearly 10,000 gallons (37,850 liters) a year in the average home, and that 10 percent of homes have leaks wasting 90 gallons (340 liters) or more every day.
How do I know what is causing my toilet to run?
- Take the lid off the tank and set it somewhere flat. Porcelain lids chip easily and are expensive to replace.
- Add 5–10 drops of food coloring, or a dye tablet if your water utility gives them away (many do, free).
- Wait 10–15 minutes. Do not flush. NYC’s Department of Environmental Protection suggests 15–20 minutes to catch slow seeps.
- Look in the bowl, then look inside the tank.
| What you see | What it means | Fix |
|---|---|---|
| Color in the bowl | Flapper is not sealing | Replace the flapper |
| No color, water trickling into the overflow tube | Water level set too high | Adjust the float |
| No color, valve hisses on and off | Fill valve failing | Replace the fill valve |
| Runs until you jiggle the handle | Chain too long or snagging | Adjust the chain |
| Color in the bowl even with a new flapper | Pitted or cracked flush valve seat | Replace the flush valve or call a plumber |
The EPA’s other quick check needs no dye at all: a healthy toilet makes refill noise only after a flush. Any hissing, trickling, or periodic refilling at other times is a leak, even a silent one you have stopped noticing.
Each part has one job. The flapper seals the tank after a flush, the fill valve refills it, and the float tells the valve when to stop. A running toilet is simply one of those steps failing to finish.
How do you replace a toilet flapper?
Denver Water identifies worn flappers as the biggest cause of toilet leaks. The flapper is a rubber or silicone flap covering the drain hole at the bottom of the tank. Minerals, chlorine, and age make it stiff and warped until it no longer seats properly, and water seeps past continuously.
- Turn off the supply valve behind the toilet, then flush to empty the tank.
- Unhook the old flapper from the two pegs on the overflow tube and unclip the chain from the flush lever.
- Take it to the store with you. Flappers are not universal: 2-inch (5 cm) and 3-inch (7.5 cm) drain openings are both common, and a mismatched flapper will leak straight away. Some toilets use a tower-style canister seal instead of a flap, which needs a part specific to that valve.
- Before fitting the new one, run a finger around the rim of the drain opening. Wipe off any mineral scale with a nonabrasive pad, since grit under a new flapper causes the same leak as a worn one.
- Clip the new flapper on, reattach the chain, and turn the water back on.
Set the chain with about half an inch (1 cm) of slack. Too tight and the flapper is held fractionally open, a leak that is very hard to spot. Too loose and it tangles under the flapper, which causes the “runs until you jiggle the handle” symptom. Trim excess chain so the tail cannot fall under the seal.
Why flappers fail early. Drop-in bleach tablets that sit in the tank are a common culprit, because the chlorine concentrates while the toilet sits unflushed and softens or warps rubber. In-bowl cleaners avoid that contact. If a flapper leaves black residue on your fingers or feels stiff rather than supple, it is near the end of its life even if it is not leaking yet.
How do you adjust the water level in a toilet tank?
If water is running into the overflow tube, the open vertical pipe in the middle of the tank, the tank is simply filling too high and spilling continuously. Denver Water lists a badly set float as the other common cause of running toilets.
The water line should sit about an inch (2.5 cm) below the top of the overflow tube. Most toilets mark it inside the tank. How you lower it depends on the valve:
- Float-cup valve (a cup that slides on the valve shaft): pinch the clip on the side or turn the adjustment rod, and move the cup down.
- Float-arm ballcock (a ball on a horizontal arm): turn the adjustment screw on top of the valve, or on older brass arms, bend the arm gently downward.
- Floatless valve (a compact valve with no visible float): turn the adjustment dial or screw, usually marked with a direction arrow.
Flush once and watch where the level stops. This fix costs nothing and is easy to overlook, because the toilet sounds like it is refilling normally. While you are there, check that the refill tube is clipped to the side of the overflow pipe rather than pushed down inside it. A tube that reaches below the water line can siphon water out of the tank and make the valve cycle.
How do you replace a toilet fill valve?
If the dye test is clean and the level is correct but the valve still cycles on and off, or hisses continuously, the fill valve has failed. This is the expensive failure if it is ignored: NYC DEP’s brochure estimates that an open fill valve can run at 3 to 5 gallons a minute, or about 3,600 gallons (13,600 liters) a day. A universal replacement fits nearly every modern toilet.
- Shut off the water, flush, and sponge out the remaining inch or so in the bottom of the tank.
- Put a towel and a bowl under the tank, because the supply line will drip.
- Unscrew the supply line, then the plastic locknut under the tank.
- Lift the old valve out, drop the new one in, and set its height so the critical level mark (or the top of the valve) sits at least an inch above the overflow tube. That gap keeps tank water from being drawn back into the supply line.
- Tighten the locknut by hand only. Over-tightening with a wrench cracks the tank, which turns a cheap repair into a new toilet.
- Reconnect the supply line, clip the new refill tube to the overflow pipe, turn the water on, and set the float as described above.
Sometimes a hissing valve only needs grit flushed out of its seal. Many valves have a removable cap for exactly this; the instructions are usually printed on it.
How much water does a running toilet waste?
The answer depends almost entirely on the size of the leak, which is why estimates vary so widely. NYC DEP sorts toilet leaks into three bands:
| Leak size | Typical sign | Daily waste (NYC DEP estimate) |
|---|---|---|
| Small | Dye appears in the bowl slowly; no sound | About 30 gallons (114 liters) |
| Medium | Occasional refill cycling or faint trickle | About 250 gallons (946 liters) |
| Large | Constant audible running | Up to 6,000 gallons (22,700 liters) |
Denver Water’s average of about 200 gallons a day sits between the small and medium bands. Silent leaks are the costly ones, because they can run for months unnoticed; the dye test makes them visible in ten minutes.
Phantom flushing. If the toilet refills briefly every few minutes or hours without anyone touching it, the tank is slowly draining into the bowl past a worn flapper and the fill valve is topping it back up. It is a slow flapper leak, and the dye test catches it.
When it is not a DIY job
Call a plumber if water is appearing on the floor around the base (that is a wax ring or a cracked tank, not a running toilet), if the shut-off valve is seized and will not turn, or if you have replaced the flapper and fill valve and it still runs. That last case usually means the flush valve seat itself is pitted or cracked, and replacing it means taking the tank off the bowl.
Repairing versus replacing the toilet
A running toilet is almost always cheaper to repair than to replace. The exception is a toilet installed before 1994, before the federal 1.6 gallons-per-flush limit. According to EPA WaterSense, toilets are the largest single source of indoor water use in a home, and the EPA’s Fix a Leak Week fact sheet notes that replacing an older model with a WaterSense labeled toilet can cut each flush from about 3.5 gallons (13 liters) to 1.3 gallons (5 liters) or less. If an old toilet also needs a new flush valve, replacement may be the better use of the money.
While the lid is off, check the fill level against the marked line and look at the flapper even if this toilet is not the one running. Fixing leaks is usually the biggest single water saving available in a house, larger than shorter showers, and larger than alternatives such as a composting toilet for an ordinary home on mains water. If your next project is outdoors, sizing a rainwater harvesting system is the logical follow-on once the indoor leaks are gone.