Direct answer: A toilet supply line usually leaks from one of three spots: the shutoff valve connection, the tank connection, or a split or corroded section of the line itself. Start by drying everything completely and finding the first wet point before you tighten or replace anything.
Most likely: Most of the time, the leak is a loose connection nut or an aging toilet supply line washer, not the toilet itself.
If the floor is wet near the toilet, make sure the leak is happening while the toilet is just sitting there under pressure. If it only leaks during or right after a flush, you are probably chasing a different problem. Reality check: water often runs down the line and drips from the lowest point, so the drip location is not always the source. Common wrong move: tightening both ends hard without drying and watching first.
Don’t start with: Do not start by reefing down on the nuts or buying a new toilet. Over-tightening can crack the tank inlet or make a small leak worse.
The line looks wet where it screws onto the shutoff valve, and the drip forms below that nut or runs down the hose.
Start here: Dry the valve body, nut, and hose completely, then watch the shutoff connection first while the toilet sits unused.
Water beads up where the supply line connects to the bottom of the tank near the fill valve shank.
Start here: Dry the bottom of the tank and the connection nut, then check whether the first moisture appears right at the tank inlet.
The hose jacket is wet or spraying, or you can see corrosion, a kink, or a split in the line itself.
Start here: Shut off the toilet water now and plan on replacing the toilet supply line rather than trying to patch it.
The floor gets damp near the toilet, but the line only looks generally wet and the source is hard to pin down.
Start here: Dry everything from the shutoff to the tank, place a paper towel under each connection, and check which one gets wet first.
This is the most common cause when the leak is small, steady, and clearly starts at one threaded connection.
Quick check: After drying the area, look for a fresh bead of water forming right at the nut, not halfway down the hose.
If the nut is snug but the connection still seeps, the sealing washer inside the toilet supply line may be flattened or damaged.
Quick check: Shut off the valve, relieve pressure, disconnect the leaking end, and inspect the washer for cracks, distortion, or missing pieces.
A braided or plastic line can leak through the hose body after years of service, kinking, rubbing, or corrosion.
Quick check: Look for bulges, rust staining, green mineral crust, frayed braid, or a wet spot in the middle of the line.
Sometimes the supply line is only carrying the water downward from a leak above or behind the nut.
Quick check: Dry the fill valve shank under the tank and the shutoff valve body itself, then watch for moisture appearing there before the line gets wet.
A toilet supply line leaks while the line is under pressure, even when the toilet is just sitting there. If the water only shows up during a flush, you are likely on the wrong repair path.
Next move: If water appears without flushing, stay on this page and trace the exact source. If the leak only happens during or after a flush, stop here and inspect for a tank-to-bowl leak, a base leak, or a drain-side problem instead.
What to conclude: You need to separate a constant supply leak from a flush-triggered toilet leak before touching parts.
The first wet point tells you whether the problem is the shutoff connection, the tank connection, the hose body, or a nearby part that is fooling you.
Next move: If one connection or one section of hose gets wet first, you now have a clear repair target. If everything looks damp at once, shut off the valve and inspect the fill valve shank and shutoff valve body more closely for seepage above the line.
What to conclude: A drip at the lowest point is often just runoff. The first wet spot is the real source.
A slightly loose nut is common and easy to correct, but only if the leak is clearly at the connection and the parts are not damaged.
Next move: If the seepage stops completely, dry the area and keep checking it over the next day. If the same connection still leaks, the washer may be damaged or the line may need replacement. If the tank connection feels unstable, stop before cracking the fill valve shank.
If the leak is from the hose body or a connection that still seeps after a careful snug-up, replacing the toilet supply line is the clean fix.
Next move: If both ends stay dry and the hose body stays dry, the repair is done. If a new line still leaks from the same tank connection, the toilet fill valve shank or its tank seal may be the real problem. If it leaks at the shutoff valve body, the valve itself needs service or replacement.
A toilet leak that looks fixed can still leave a slow seep. Final checking keeps you from finding out later after the floor has stayed wet for hours.
A good result: If the line and both connections stay dry through a sit test and a refill cycle, you have likely fixed the leak.
If not: If moisture returns and it is not clearly from the line, stop guessing and move to the exact next repair path or bring in a plumber.
What to conclude: A successful repair stays dry under pressure and after refill. Anything else means the leak source was different or there is more than one leak.
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Sometimes, yes, if the leak is clearly at a connection and the nut is only a little loose. Use a careful snug-up, not brute force. If it still seeps, the washer or the toilet supply line is usually the real issue.
Water often runs down from a leaking connection and makes the middle look guilty. Dry the whole line and watch for the first wet point. If the middle gets wet first, the hose itself is failing and should be replaced.
Usually no. Most toilet supply line connections seal with a washer inside the connector, not with thread sealant. If it leaks, the fix is usually proper alignment, careful tightening, or a new toilet supply line.
They can last for years, but age, kinks, corrosion, and repeated movement shorten their life. If the line is old, stiff, rust-stained, or already seeping, replacement is cheap insurance compared with floor damage.
If the new line was threaded on by hand and tightened correctly, look closely at the toilet fill valve shank under the tank or the shutoff valve body. At that point the line may not be the problem anymore.
No. A base leak usually points to a wax ring or toilet movement issue, and it often shows up during or after flushing. A true toilet supply line leak happens on the pressure side and can drip even when the toilet has not been flushed.