hard water is not detrimental to a wooden tub, we just recommend to avoid circulation systems

Thank you for your interest in our japanese bathtubs.
With reference to your kind question, also in japan there are many places with hard water.
Considering that in the onsen (japanese hot-springs) with thermal water containing all sorts of minerals wooden baths are used,
we can say that there is not too much to be worried about.

The scaling occurs if the water is left in the tub for long periods (es. using recirculation systems) so we would recommend to fill the tub only when in use (which works for most residential applications).
I am not a chemist, so forgive my lack of technical terms, but actually calcium tends to build up on metals or enamel, it does not stick to wood.

We are looking forward to working with you and remain at your disposal for any other question of problem.