Dual flush toilet

Lore & Background

The dual flush toilet was first developed by Japanese manufacturer TOTO in 1960, featuring two levers and a built-in hand-washer that reused water for flushing. However, it did not achieve commercial success in Japan or internationally. In 1976, American industrial designer Victor Papanek proposed the dual flush system in his book Design for the Real World, but the first practical implementation came in 1980 from staff at Australian company Caroma, with flush volumes of 11 and 5.5 litres. A redesign in 1994 reduced water usage to 6 and 3 litres.

The dual-flush toilet relies on gravity rather than siphoning to remove waste, requiring less water and resulting in a lower waterline. It uses a larger 10 cm trapway for efficient bowl clearing. Mechanisms include push-button (two buttons for different volumes), lever (with a half-flush if the handle is held or released immediately), and tipping bucket (operating in dual flush mode when the lever is rotated halfway).

The design became almost universally adopted in Australia, New Zealand, Singapore, Sweden, Israel, and many other countries, often mandated by legislation for new buildings. The more complex mechanism is more expensive than many other low-flush toilets.

Reader's Guide

The dual flush toilet represents a significant innovation in water conservation, reducing water usage by offering two flush volumes for liquid and solid waste. Its development began with TOTO in 1960 but only gained practical traction with Caroma's 1980 design. The technology has been widely adopted in numerous countries, often supported by government mandates and rebate programs, such as Australia's 'Target 155' campaign and state rebates in Victoria, New South Wales, the ACT, and South Australia. In the United States, the Energy Policy Act of 1992 set a maximum of 6 litres per flush, and the WaterSense label requires an average flush volume below 4.8 litres. However, not all dual-flush toilets meet this standard; some have flushes of 6.1 and 4.8 litres, which do not qualify. Additionally, dual flush mechanisms are more prone to leaks than traditional siphons, and a 2020 claim by UK supplier Thames Water suggested that leaks and user confusion may cause water wastage. Despite higher initial purchase and installation costs, retrofitting existing toilets is possible for about US$30. The dual flush toilet's legacy is its role in reducing water consumption, though its effectiveness depends on design and user behavior.

Did You Know?

• The first dual flush toilet was developed by Japanese manufacturer TOTO in 1960 but was not commercially successful.
• The first practical dual flush toilet was designed in 1980 by staff at Australian company Caroma, with flush volumes of 11 and 5.5 litres.
• In the United States, a dual-flush toilet must have an average flush volume below 4.8 litres to receive the WaterSense label.
• UK supplier Thames Water claimed in 2020 that dual flush toilets may waste more water than they save due to leaks and user confusion.