Not necessarily due to the automatic vs. manual distinction but the mechanical design of the valves. "While the precise reasons for the higher bacterial growth

Not necessarily due to the automatic vs. manual distinction but the mechanical design of the valves. "While the precise reasons for the higher bacterial growth in the electronic faucets still need clarification, the researchers say it appears that standard hospital water disinfection methods, which complement treatments by public utilities, did not work well on the complex valve components of the newer faucets. They suspect that the valves simply offer additional surfaces for bacteria to become trapped and grow."