Saving water not only lowers your utility bill, it also has a beneficial effect on the environment. In a joint study sponsored by Southern Water and the Environment Agency in the United Kingdom, the Water and Environmental Journal stated, "The use of water for toilet flushing accounts for about 30% of household consumption, thereby offering considerable potential for water saving." Think "green" and take a few minutes to reduce the water level in your Fluidmaster cistern to the lowest possible level consistent with efficient flushing.
Shut off the water supply to the toilet by turning clockwise the handle on the valve below the toilet tank. Lift the tank lid off and place it on one side.
Insert a flat screwdriver into the slot on top of the water level adjustment rod. This rod is connected to the upper cap assembly on top of the mechanism. Twist either way and retain tension on the screwdriver. Move the lug attached to the black float cup up or down the rod to adjust the cistern water level. Release the tension on the screwdriver. This applies to the Fluidmaster model 400UK. For instructions on the Fluidmaster model 400A, go to the next step.
Hold the water level adjustment rod hooked onto the upper cap assembly arm. Squeeze the retaining clip lower down the rod with the other hand. Move the retaining clip connected to the black float cup up or down on the rod as required.
Refill the cistern by turning the supply valve back on. Test-flush with a handful of wadded toilet paper. Although Fluidmaster marks the recommended water level with a line on the inside of the tank, experiment with progressively lower levels until reaching the minimum amount of water consistent with efficient flushing. Replace the tank cover when finished.