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Toilet Tank Leak Check

Answer what you have seen and get the likely causes, what to do first and who to contact. It never asks you to take the tank apart.

See the likely causes

Answer from what you have seen. This only looks at what you can observe and at the dye test from the US EPA WaterSense leak guide. It does not tell you how to take parts apart or replace them. Nothing you choose is saved or sent.

Is any of this happening right now? (optional)Water keeps pooling and spreading on the floorSomeone below told you water is coming through their ceilingThe toilet bowl is about to overflowAn outlet or electrical item is near the wet floor

1. When does water run?

2. Water level in the tank

3. Dye test

4. The floor

5. The shutoff valve

6. Where you live

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Example

A toilet that refills by itself, with the water below the overflow tube, color showing in the bowl after the dye test, a dry floor and a working shutoff valve points to a leaking flapper. If you rent, tell your landlord before any repair. Press “Load an example” to try it.

How it works

The dye test comes from the US EPA WaterSense leak guide: put a few drops of food coloring in the tank, do not flush for 5 to 10 minutes, and if color shows in the bowl the flapper or drain seal at the bottom of the tank is leaking. Flush afterward so the dye does not stain.

The tool also looks at the water level, the floor, the shutoff valve and where you live, and gives priority to anything urgent such as water spreading, a leak to the unit below or an outlet near water. It stops at closing the shutoff valve and does not describe how to take parts apart or replace them.

Frequently asked questions

Where is the shutoff valve?

It is usually on the wall or floor behind or beside the toilet, where the small supply pipe comes out. Turning it clockwise closes it. If it will not turn, do not force it.

Can I fix a leaking flapper myself?

This tool does not give repair steps. Tell your building manager or a plumber what you saw, such as the dye result, and ask who should do the repair.

What if water is near an outlet?

Do not touch the outlet or anything plugged into it. If you worry about shock, switch that circuit off at the breaker and have an electrician check it after the floor is dry.

Sources and last updated

Dye test: US EPA WaterSense, “Free of Leaks” technical sheet, https://www.epa.gov/system/files/documents/2023-08/ws-homes-TRM-1-FreeofLeaksTechSheet.pdf (checked 2026-10-26). The grading rules are the same as on the Korean version of this tool.
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Last updated: 2026-10-31 · 한국어로 보기