WASHLET – The Innovation that changed Japan’s bathroom culture – Part 2

Challenges in product development

The decision to develop a new product meant we had to face a series of complex challenges. The first was determining the precise position for the water spray nozzle. In other words, we needed to find the optimal location for the cleansing spray. However, there was no data source available to help us with this. So, we came up with the idea of stretching steel wires across the toilet seat, and asked colleagues within the company to sit down and mark the position of their “rear” using paper, to collect data on where to target the spray.

It was understandably awkward to ask people for such a sensitive favor. The most polite refusals we received made it clear that—even among close colleagues—sharing that kind of personal information was off-limits, especially for female staff. However, thanks to our passion and persistence, we eventually persuaded around 300 people—both men and women—to take part in the project.

The next challenge was determining the ideal warm water temperature that would provide a pleasant and relaxing experience. Our development team tested it firsthand by gradually increasing the water temperature in 0.1-degree increments, taking turns to test the spray continuously for 16 hours a day to gather data. Some testers jumped up from the seat, thinking they had been burned by the high water temperature. We also conducted tests to determine the optimal temperature for use in climates ranging from as cold as -10°C to as warm as 30°C. After many trials, we concluded that the optimal temperature was: 38°C for the water, 36°C for the seat, and 50°C for the drying air.

Then came the challenge of finding the perfect spray angle suitable for all users. Our experiments showed that a 43-degree angle was ideal. (At that time, most bidet seats on the market had a fixed 28-degree spray angle.) This “golden angle” ensured effective cleansing for all users while also preventing backflow of used water into the nozzle.

But the challenges didn’t stop there. The biggest hurdle was maintaining the water temperature consistently at 38°C. Our first solution involved using a bimetallic thermal switch.

This switch is a disc-shaped piece of metal made by bonding two metal strips with different thermal expansion rates, then pressing and punching them into circular or polygonal shapes. When heated, the metal bends; when cooled, it returns to its original shape. We tried using this mechanism to control temperature by transferring the bending motion through a ceramic actuator in the WASHLET, but it proved too unstable for maintaining a constant temperature.

Someone then suggested using an IC (integrated circuit) chip. We consulted a home appliance manufacturer, but they responded with concern: “Using an IC chip in direct contact with water is insane—don’t you realize how dangerous an electric leak could be?”

Despite this, our development team did not give up. We immediately ordered IC chips and focused all our efforts and expertise on designing and prototyping a safe control circuit for water temperature. During testing, one researcher accidentally touched the chip with his elbow, receiving a 100-volt shock. The development process was so risky that it could have cost us our lives. A single mistake could endanger both developers and users, pushing the entire project to the brink of collapse. And then came a breakthrough…

One rainy day, while waiting at an intersection, a team member noticed that the traffic light was still functioning perfectly despite the downpour. In that moment, inspiration struck.

He rushed to a traffic signal manufacturer, where he learned that they used a special waterproof coating on IC chips called Hybrid IC technology. After negotiations, the two parties agreed to collaborate: the manufacturer would be able to promote its Hybrid IC technology more broadly, while TOTO would gain a safe solution for water temperature control.

As soon as we received the first batch of Hybrid ICs, we installed them into pre-built control circuits, sealed them with plastic covers, and tested them by spraying saltwater (to simulate urine) onto the circuit. The test was successful—no electric leakage occurred. At last, we had resolved the electrical safety issue.