This is one of the worst daily use product designs that is prone to human error.

A single-lever mixer tap is normally used for a basin and shower in a centralized hot water supply system, often found in almost 4-star and above hotels.

I think most of us are annoyed with this design. It is quite challenging to mix the volume of hot and cold water until it reaches the comfortable bath water temperature, sometimes wasting a lot of water while adjusting the coarse and tight single-lever design. Human error might occur when the tap control could not be properly measured, thus mistakenly putting the wrong ratio of hot water above the appropriate temperature (37-38°C), consequently harming the user.

The probability of human error will escalate when users use it for the first time, and worsen if they naturally have lower guesstimation ability, especially among children, elderly, and disabled users.

When adjusting the water temperature, the users cannot stand directly under the shower head to avoid their bodies from freezing or boiling water. What would happen if the shower screen is designed with insufficient space allowance?

The single-lever tap design will introduce another cause of human error if the direction of the hot-cold water position is set in the opposite direction with convention – hot is left and cold is right (there is also an up and down handle). Or perhaps the design uses a different color code than the convention one – hot is red and blue is cold [1].

Yes, I found so many cases. The shower tap was correctly designed for cold (right) and hot (left), but the sink faucet was designed on the opposite side which was cold (left) and hot (right). It happened in the same washroom. Users could easily get confused and exposed to the hot-water hazard.

Before you select the tap design based on aesthetic appearance, please also consider the operational and safety concerns.

[1] These specifications are outlined in SPAN – Technical Specification: Water taps – single and combination taps

M. Hafizul Hilmi
Technip Energies