> why would anyone ever wash their hands with cold water.
Well it depends on the time of the year. In winter, you certainly don't use them that much because water is freezing cold. But as soon as it turns april-may, water becomes lukewarm or even relatively hot in summer months (summers are excruciatingly hot in Japan), so then it's not an issue anymore.
> And maybe I am illusioned by the effectiveness of warm water.
Do you mean warm water is more effective at washing ? There's actually no basis for that. Surfactants matter more than temperature.
Well it depends on the time of the year. In winter, you certainly don't use them that much because water is freezing cold. But as soon as it turns april-may, water becomes lukewarm or even relatively hot in summer months (summers are excruciatingly hot in Japan), so then it's not an issue anymore.
> And maybe I am illusioned by the effectiveness of warm water.
Do you mean warm water is more effective at washing ? There's actually no basis for that. Surfactants matter more than temperature.