Q. I usually take a shower to comply with tisha kavim, I do this Erev Shabbos too. Can I do this during all the nine days or only in erev Shabbos? Can the water be warm?
A. Many Poskim maintain that you comply with the custom of Nine Kavim (as an alternative to Tevilas Ezra, see Mishna Berura 88: 4) by showering until that amount of water (approximately 23 to 32 liters) cascades on you. (Minchas Yitzchok 4: 21, Yaskil Avdi 7: p. 387, Taharas Yom Tov 19, Chelkas Yakov 3: 61, Minchas Oviv p. 202 et. al. However, Mishne Halochos 3: 1-7 and others disagree)
Mishna Berura (O.H. 551: 97) quoting Chaye Adam permits using hot water for washing (head, hands and feet) on erev Shabbos Chazon for one who always does so.
Eishel Avrohom, Aruch Hashulchan (ibid.), Mishpotecha L'Yaakov (40,) Nitey Gavriel (1: 42 11 and note 17) quoting Chazon Ish permit daily immersing a mikva before davening during the Nine Days, if one always immerses.
Horav Shlomo Miller's Shlit"a opinion is that the same applies to one who uses a shower for Tisha Kavim compliance. If he constantly observes Tisha Kavim, he would be permitted to shower with tepid water during the Nine Days. However, if he regularly omits showering on Shabbos given that the water would then be completely cold, he would not be permitted showering during the Nine Days.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit"a.
Important Numbers
