To raise the water level in a toilet tank, you adjust the fill valve — the mechanism inside the tank that controls how high the water fills after each flush. On most modern toilets with a float-cup or tower-style fill valve, you turn an adjustment screw or squeeze a clip and slide the float up. On older toilets with a ball-float (the balloon-on-an-arm style), you bend the arm slightly upward or adjust the adjustment screw where the arm connects to the fill valve. The correct water level is typically about one inch below the top of the overflow tube — a marking is often printed on the overflow tube or inside the tank for reference.

Why the Water Level Matters

The tank water level determines how much water enters the bowl with each flush. If the level is too low, the toilet gets an incomplete flush — waste doesn’t clear fully, and you find yourself flushing twice. If the level is too high, water spills continuously over the top of the overflow tube and runs straight into the bowl and down the drain — an invisible but significant water waste that shows up on your bill. The correct level provides a full, effective flush without wasting water.

Toilets are designed to deliver a specific flush volume — modern WaterSense toilets use 1.28 gallons per flush or less. That volume is calibrated to the fill level. A fill level even half an inch low can meaningfully reduce flushing effectiveness in a high-efficiency toilet, while a level too high wastes water constantly and can also cause the fill valve to run intermittently as it works to maintain an unachievable set point.

Identifying Your Fill Valve Type

Look inside the tank. You’ll find one of three common valve types:

  • Float cup / tower fill valve (most modern toilets): The float is a cup or collar that rides up and down on the vertical valve body. Adjustment is typically done by turning a screw on top of the valve (clockwise to raise the water level) or by squeezing the release clip on the side of the float and sliding it up or down the valve shaft.
  • Floatless / pressure-sensing fill valve: Found in some newer models, these have no external float — they sense pressure at the bottom of the tank. Adjustment is made with a screw on top of the valve. Consult your toilet’s manual for the specific procedure.
  • Ball float (older toilets, pre-1990s): A ball on an arm connected to the fill valve. To raise the water level, bend the arm upward slightly — gently, as the arm is often plastic and can crack — or turn the adjustment screw where the arm attaches to the valve body. Some have a brass arm that can be bent more confidently.

Step-by-Step: Adjusting a Float Cup Fill Valve

This is the most common type in Denver homes built in the last 25 years. You do not need to turn off the water supply for a simple adjustment — just work with the tank as is.

Remove the tank lid and set it aside carefully — porcelain tank lids are heavy and chip easily. Look at the overflow tube and find the water level mark (typically a line or the letters “WL” stamped into the tube, or a mark on the tank wall). The water should sit about one inch below the top of the overflow tube opening.

If your level is low, locate the adjustment mechanism on the fill valve. On a Fluidmaster 400-series valve (extremely common), turn the adjustment screw on top of the valve clockwise to raise the cutoff point. On a valve with a clip-and-slide float, squeeze the clip ears together, slide the float up, and release. Flush the toilet once to let the tank refill to the new set point, then check the level. Repeat as needed until the water stops about an inch below the overflow tube rim.

When Adjustment Doesn’t Fix the Problem

If you raise the fill valve adjustment but the water level still comes up short, the fill valve itself may be failing — its internal seal or diaphragm can wear out and prevent the valve from fully opening. A fill valve replacement is an inexpensive repair, and the valves are widely available at hardware stores. If you’re not comfortable with that repair, a plumber can handle it quickly. Similarly, if the tank refills to the correct level but the toilet still flushes poorly, the issue may be with the flapper or the rim jets in the bowl rather than the water level.

When to Call Done

Toilet adjustments and minor repairs are within most homeowners’ comfort zone, but if the tank is cracked, if water is leaking at the base of the toilet, or if adjustment doesn’t solve persistent flushing problems, it’s time for a professional look. Done’s plumbing team handles toilet repairs, fill valve and flapper replacements, and full fixture upgrades across the Denver metro. Visit our kitchen and bath plumbing page for details, or reach out through our plumbing services page to schedule a visit.