What is a Toilet Cistern

Most household toilets have two primary structural components to them: the bowl and the cistern. The toilet cistern is the upper portion of the toilet that holds water for when it needs to be flushed. Most people refer to the toilet cistern as the “tank.”

On a modern toilet, the cistern is mounted above the toilet bowl and close-coupled to it. In the past, the tank was sometimes placed higher above the toilet and connected to the bowl by a pipe. Sometimes, the cistern was placed next to the toilet, but still above the bowl, so it could be disguised by decorations or cabinetry.

What to Expect from a Toilet Cistern

The cistern fills with water based on three elements: a supply line, a fill valve, and a float mechanism. The supply line is connected to the base of the cistern, allowing water from the pipes in the walls to fill the tank to an appropriate level.

The fill valve allows water from the supply line to enter the tank for storage when it is open. When the fill valve is closed, then water remains at the ready to enter the tank, but is prevented from doing so until the valve opens once again.

As for the float mechanism, it registers the level of water that is inside the tank. Based on its position, it will allow the fill valve to open or close. This allows water to enter the tank whenever levels become too low.

How the Toilet Cistern Operates

The cistern passes water through to the toilet bowl, either by gravity or an air pressure assist, to create a flush. The flush is initiated by the user in some way. For homeowners, a lever or a button is what typically activates the mechanism. Commercial and industrial toilets sometimes offer a motion sensor so a hands-free experience can be had by the user.

Once the toilet flushes, the float mechanism inside the cistern lowers. This tells the fill valve that water needs to be added to the tank. The valve opens, taking water from the supply line that has been waiting. This allows the cistern to refill.

Some models offer a half-tank flush, which is a low-water flush for liquid waste.

By understanding how the toilet cistern works, it becomes easier to maintain the modern toilet. Technologies may have evolved, but the principle of a good flush has remained the same.