if these instant water heater are so vulnerable to water i dont understand why they are located inside the bathroom......
they should be self contained in a sealed box outside the bathroom away from any pipes or water source as possible.
Economy and ease of fitting counted for home-appliances; like instant water heater.
Otherwise, our HDB will be fitted with Condo-style water heater, where it is located about false ceiling.
In Taiwan, most households use gas-fire water heaters.