How to Adjust Toilet Water Level
Updated February 20, 2026
Raise or lower your toilet tank water level to fix weak flushes, stop a running toilet, or cut water waste -- covers ball floats and cup floats in 5 minutes flat.
Overview
Weak flush that barely clears the bowl? Or a toilet that keeps running after every flush? Nine times out of ten, the water level in the tank is off. Too low and you do not get enough water for a complete flush. Too high and water spills over the overflow tube into the bowl nonstop -- that is what causes the running sound. The target is about 1 inch below the top of the overflow tube. Adjusting it takes 5 minutes, costs nothing, and you might not even need a tool. The method depends on whether you have a ball float (older toilets) or a cup float (modern Fluidmaster-style valves).
What You'll Need
Safety First
- You do not need to shut off the water for this. The water in the tank is clean supply water and you are just adjusting the float. That said, if reaching into a full tank of water is not your thing, go ahead and turn off the supply valve and flush first.
- The tank lid is heavier than it looks -- solid porcelain that will crack or shatter if you drop it. Set it flat on a towel on the floor. Never balance it on the edge of the tank or on the toilet seat.
Step-by-Step Instructions
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Remove the Tank Lid and Check the Current Water Level
Lift the tank lid straight up and set it on a towel on the floor. Look inside and find the overflow tube -- it is the tall open-topped tube in the center of the tank. That is your reference point. The water should sit about 1 inch below the top of that tube. If water is flowing over the top and into the bowl, the level is too high. If it is well below the 1-inch mark, it is too low. Grab a marker and put a line on the tube at the 1-inch-below point so you have a clear target to adjust to.
Tip: Check the overflow tube for a molded line marked 'WL' or 'WATER LINE' -- many manufacturers emboss the ideal level right on the tube. If it is there, use that instead of measuring. -
Identify Your Float Type
Two types of floats, two different adjustment methods. A ball float is a round ball -- usually black or brass -- attached to a long horizontal arm. You will see these on older toilets. A cup float is a cylindrical plastic piece that rides up and down on the fill valve shaft. That is the modern Fluidmaster-style setup and what most toilets made in the last 20 years use. Figure out which one you have and skip to the right step below.
Tip: Quick way to tell: if you see a tall vertical assembly on the left side of the tank with a cylinder sliding up and down it, that is a cup float. If there is a horizontal arm sticking out with a ball on the end, that is a ball float. -
Adjust a Ball Float
With a ball float, you are literally bending a metal arm. Bend it up to raise the water level, down to lower it. A quarter inch of bend in the middle of the arm makes a noticeable difference, so go easy. Some newer ball floats have an adjustment screw where the arm meets the fill valve -- clockwise raises the level, counterclockwise lowers it. After adjusting, flush and let the tank refill. Check if the water stops at your target mark. If not, tweak it again.
Tip: Grip the arm near the middle when bending -- not at the ends. Bending at the connection point or at the ball can crack things. Old brass arms bend easily. Newer plastic arms usually have a screw or clip adjustment instead. -
Adjust a Cup Float
For a cup float, look for a spring clip on the side -- squeeze it and slide the float up to raise the water level or down to lower it. Some models use a screw on top of the fill valve instead: clockwise raises the level, counterclockwise lowers it. Move it about half an inch at a time. Flush, let the tank refill, and check the level against your mark. Keep adjusting until the water stops about 1 inch below the overflow tube.
Tip: If the float is stuck and will not slide, mineral deposits are probably binding it to the shaft. Wipe the shaft down with a vinegar-soaked cloth and try again. The adjustment screw on top of Fluidmaster valves is a flat-head you can turn by hand or with a screwdriver. -
Test and Verify the Flush
Flush 2-3 times and make sure the tank fills to the right level each time and the fill valve shuts off cleanly -- no running water sound after the tank is full. If it was running before, wait 15-20 minutes and check that the level has not dropped. That confirms the valve is actually shutting off. If the flush was weak before, test that it clears the bowl completely now. Still weak despite the correct water level? The problem is probably clogged rim jets or a partial blockage in the trap, not the water level.
Tip: If the fill valve will not shut off no matter where you set the float -- it keeps running or cycles on and off -- the valve itself is shot and needs replacement. A Fluidmaster 400A is $8-15 and takes about 15 minutes to swap out.
Pro Tips
- The 1-inch rule is a guideline, not gospel. If your toilet flushes great at 1.5 inches below the overflow and you want to save water, leave it. If it needs to be closer to the tube for a solid flush, that works too -- just never let the water actually reach the overflow or you will have a running toilet.
- Want to conserve water but the flush gets too weak when you lower the level? Split the difference -- drop it half an inch instead of a full inch. Every fraction of an inch is roughly 0.1-0.2 gallons per flush, so even a small change adds up over time.
- Water level can shift with seasonal pressure changes. Municipal pressure runs higher at night and lower during peak hours. If the toilet only runs at certain times of day, a slight float adjustment usually fixes it.
- While the lid is off, take 10 seconds to check the flapper for wear and the chain for proper length. Those are the other two most common causes of toilet problems and you are already right there looking at them.
- Pressure-assisted toilet with a sealed tank inside the porcelain one? Do not touch the water level. Those systems are factory-set and need specialized knowledge to adjust. Call the manufacturer or a plumber.
When to Call a Pro
You will never need a plumber just to adjust the water level. But if the fill valve will not shut off at any setting, it needs replacement (easy DIY or a quick plumber visit, $8-15 for the part). If the flush is still weak at the correct water level, there may be a blockage in the trap or clogged rim jets that a pro can clear. And if you have a pressure-assisted system, call the manufacturer.