What are the parameters for taking a shower during the 9-day period between Rosh Chodesh Av and Tisha Bav? Namely:
- When is one allowed to?
- When doing so what water temperature should it be set on?
- Can one use soap or shampoo?
In the time of the Shulchan Aruch part of the mourning process during the Shloshim was not to bathe. As such, The Shulchan Aruch (Orach Chaim 551:16) records a custom practiced by Ashkenazim of not bathing or showering during the Nine Days.
However, nowadays the custom is to shower immediately after Shiva (and not to wait for the Shloshim to end). Therefore these days one may bathe during the 9 days.
This would seem to indicate that there are no restrictions to the bathing.
On the other hand, many are a much more strict. Some differentiate between bathing for pleasure and bathing for necessity (Kavod Habriyot). They say that while we may bathe, we should minimize our frequency, length and comfort.
Erev Shabbos Chazon (Shabbos before Tisha B'av) Shulchan Aruch says you can bathe with warm water, because it is a Mitzvah.
Sefardim only follow the mourning period during the week of Tisha B'av.
R. Yitzchak Abadi discusses this in a responsum:
ואגב דעסקינן ברחיצה לא אוכל להתאפק מלהעיר על מנהג של הרבה אנשים אשר לא מתרחצים מר"ח אב עד העשירי בו וחושבים שלרחוץ הוא איסור גמור וגורמים בזה לנזקי שכנים וחלול ה' העולה על כולנה כי למרבה הצער בימים אלה החום גובר והזיעה מתרבה והריח נודף וא"א לעמוד גם מחוץ לד' אמותיהם ולפעמים מתכנסים למקום צבור בבית הכנסת וכדומה וכן באוטובוסים וקשה לעמוד שם בגלל זה ואין צורך להאריך בגריעות הדבר ובחילול ה' הגדול שיש בדבר זה
והנה מפורש בשו"ע שכל הרחיצה שאסורה הוא רק ברחיצה לתענוג אבל להעביר הלכלוך והטיט מותר ואני מוסיף שזה גם מצוה וודאי שמותר וצריך להשתמש בסבון וכל דבר שמנקה היטב ובמים חמים ורחיצה של תענוג נקרא שהולכים לבריכת מים או לים וכדומה לזה
And since we are dealing with washing, I cannot hold back from pointing out bout the custom of many people that they don't wash [shower] from the first day of Av until the tenth day, and they think that washing is an absolute prohibition. And by this they cause harm to neighbors, and a desecration of God's name above everything, because unfortunately during these days the heat rules and the sweat abounds and the odor flows and it is impossible to stand even outside of four amos from them. And sometimes they enter into a public place in the synagogue or the like, and also on buses, and it is hard to stand there on account of this. And there is no need to elaborate about the badness of the matter and about the great desecration of God's name that there is in this matter.
And behold it is explicit in Shulchan Aruch that the entire washing that was forbidden is only washing for enjoyment, but removing the dirt and the grime is permitted. And I add that this is even a mitzvah. It is certainly permitted. And one must use soap, and everything that cleans well, and hot water. And "washing for enjoyment" refers to going to a pool of water, or the sea, or the like.
The Kovetz Halachos pg. 183:1 writes that the minhag is one should not wash his whole body starting from rosh chodesh and on even in cold water. However, parts of the body which get dirty and one usually washes those areas to get rid of the dirt then it’s permitted to wash those areas with cold water. In halacha 4 he writes that a person who is more finicky (istanis) who showers everyday then maybe one can be lenient and wash with cold water [the most cold he can handle] and soap. In halacha 5 he writes that one who always takes a hot shower l’kovod shabbas may do so on erev shabbas with soap.
Rav Belsky in Shulchan Halevi 16:1 writes that washing that is prohibited during the nine days is specifically talking about pleasurable washing. However, when one is dirty and all sweated up one can wash off the dirt and sweat and if needed then soap can be used, but one must be careful to quickly wash up and not stay to the point of enjoyment. The Aruch Hashulchan 551:37 notes that one who is not clean may wash even in hot water in order to get clean. The Salmas Chaim siman 219 writes that using shampoo and hot water is not prohibited as long as it’s done solely for cleanliness and not done for pleasure.
The answer is that it depends - see this excellent comprehensive article by rabbi spitz explaining all the reasons and backgrounds as well as contemporary poskims' relevant psak:
Basically, as long as the showering is strictly for hygiene, it is permitted - but one must take steps to minimize his pleasure: as cold as one can bear, quickly, and only use soap and shampoo when needed.