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.
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.
The Sephardic tradition maintains that the mourning period only exists during the week of Tisha B'av. Therefore, during a year like this (5772), where Tisha B'Av falls out on a Sunday, there is no prohibition whatsoever (according to the Sephardic tradition) to shower using warm water / soap / shampoo since the week before is not the week of Tisha B'Av. There is no such thing as "the nine days" according to the sephardi tradition, as stated in my first sentence to this answer.