Hope the Rav is doing well! My children have coughs and cool air humidifiers seem to help their coughs. Can one run a humidifier on Shabbos? There is no electricity involved other then the on bottom. It sounds like a fan. Can one refill the water once it eventually evaporates? One can not see the water turning into vapor but it does help the air for coughs.
Answer:
For children who are ill it is certainly permitted to add water.
Even without extenuating circumstances, it seems that it is permitted to do so, though some are stringent.
Best wishes and warm regards.
Sources:
The Minchas Yitzchak (7:21) raises the question of humidifiers, and writes that there is room to be stringent on account of the prohibition of nolad, though he appreciates that this is not a classic case of nolad because the water is being divided and not boiled. [He adds a concern that the machine will shut down if water is not added.]
Or Le-Zion 2, 41:6, however, rules that it is permitted to use the humidifier, because no act of labor is involved.
The division of the water raises the concern for the Yerushalmi, which discusses (and prohibits) the separation of water by means of the wind. However, authorities have already limited the application of the Yerushalmi (see Magen Avraham 446:2 (and Mishnah Berurah 6) and Biur Halachah 319 citing from Rabbi Akiva Eiger 20; see also Shulchan Aruch Ha-Rav 446 in K.A. 3), and authorities generally don’t understand why splitting water by means of wind should involve any melachah.
This is the reason why authorities have permitted the use of spray cans (though for spray cans there are still greater grounds for leniency), and it is therefore permitted to add water, certainly for the purpose of sick children. This is also the ruling given by the Orchos Shabbos.
