A cistern is the tank that holds water for flushing a toilet. It’s usually mounted just above the toilet pan and connected by a flush pipe, although in some designs it may be concealed within the wall or attached directly to the pan. The cistern is a key part of the flushing system, storing enough water to clear waste from the bowl and refill the trap seal.
How cisterns work
When you press the flush button or pull the lever, the cistern releases water through the flush pipe into the toilet bowl. This rush of water removes waste and transports it through the drainage system. Once the cistern empties, a valve opens to allow water to refill the tank. A float inside the cistern rises with the water level, shutting off the supply once it reaches the set height.
Most modern cisterns in Australia feature a dual-flush mechanism, allowing you to choose between a full flush and a reduced flush. This helps conserve water and is now standard under AS/NZS 6400 water efficiency labelling requirements.
Types of cisterns
Cisterns come in several styles to suit different toilet installations:
- Close-coupled cisterns – These sit directly on the back of the toilet pan, forming a compact and tidy unit.
- Link or connector cisterns – These are mounted slightly higher and connected to the pan with a short flush pipe.
- Concealed or in-wall cisterns – Hidden behind the wall or inside a cabinet, these create a clean, minimalist look, often paired with wall-hung toilets.
- High-level cisterns – A more traditional style, these are mounted high on the wall with a long flush pipe and chain pull.
Materials and finishes
Cisterns are most commonly made from ceramic, vitreous china or high-grade plastic. Plastic cisterns are lightweight, durable and resistant to cracking, while ceramic options tend to offer a more solid, traditional feel. For concealed installations, the cistern body is usually plastic, as it doesn’t need to be visible.
The external finish may match other bathroom fittings and can be white, coloured or patterned. In-wall models may have only a visible flush plate, which can be stainless steel, chrome or another decorative finish.
Water efficiency
Choosing a cistern with a high water efficiency rating can significantly reduce household water use. Dual-flush systems typically use around 3L for a half flush and 4.5–6L for a full flush, depending on the design. Look for products carrying the Water Efficiency Labelling and Standards (WELS) label to compare performance.
Upgrading an old single-flush cistern to a dual-flush model can save thousands of litres of water each year. Some older pans may need to be replaced at the same time to ensure compatibility and optimal performance.
Maintenance and repairs
Cisterns are generally low maintenance, but may require attention if:
- Water continues running after flushing (often due to a worn-out inlet or outlet valve)
- The cistern doesn’t refill properly
- The flush button or lever sticks
- Leaks occur at the flush pipe connection or inlet
Many of these issues can be fixed by replacing internal components such as washers, valves or the float mechanism. If your cistern is old or cracked, replacing the entire unit might be more economical. Regular checks can prevent leaks and water waste.
