Types of Fill Valves on Low-Flow Toilets

Traditional and some low-flow toilets use a ballcock fill valve. The ballcock fill valve, also known as a float valve, has a long valve stem connected to a float ball or float cup, depending on the model. When you flush the toilet, the float lowers as the water enters the bowl. As the valve fills the tank, the float rises. When the float reaches a set level, the valve stops filling the tank. (See Reference 5)

Many low-flush toilets use pilot-fill valves instead of ballcock fill valves. Pilot-fill valves don't have a long valve tube or a float. Instead, the valve assembly fits directly over the water input pipe and has a separate tube attached to the water over-flow pipe inside the tank. Pilot-fill valve assemblies have an adjustable knob that allows you to control the flow of water into the tank. (See Reference 2)

Pilot-fill valves may do a better job of conserving water than traditional ballcock fill valves. Since pilot-fill valves have adjustable controls, turning the dial to a lower setting prevents the tank from using more water than needed per flush. However, toilets with ballcock fill valves may qualify for the WaterSense label, a high-efficiency standard set by the EPA, providing the fill valve passes a performance test. For example, the valve must not overfill the toilet or surpass the fill level recommended by the manufacturer. (See Reference 2)

The EPA tests other aspects of the toilet, such as flush volume and waste removal. For example, the effective flush volume can't exceed 1.28 gallons, and waste removal must be 350 grams or higher, according to the EPA. (See Reference 2) Many toilets conserve water effectively without meeting the WaterSense requirements, but WaterSense toilets have the most efficient water consumption features.