Question: May the floors of the house be washed with water on Shabbat?
Answer: The Gemara (Shabbat 95b) explains that our Sages forbade washing the floors of the house on Shabbat because in their times, the floors of the house were not surfaced as they are today; rather, they covered the floor of the house with sand or earth. For this reason, our Sages even forbade sweeping the floor on Shabbat so that one does not flatten the floor of the house, which is forbidden on Shabbat, as a result.
Nevertheless, the Gemara and Poskim write that when the floor of the house is surfaced, one may sweep the floor on Shabbat. Our Sages ruled leniently on this matter even when most houses in the city have unfinished floors as long as that specific house has finished floors since this is truly necessary. However, our Sages never permitted washing the floors even when the house has surfaced floors.
Nonetheless, when most houses in the city have finished floors, our Sages allowed even sprinkling some water on the floor. This is indeed the opinion of the Rambam (Chapter 1 of Hilchot Shabbat). On the other hand, some other great Rishonim rule completely leniently in this regard and allow even washing all the floors of the house with a large amount of water, as long as most houses in the city have surfaced floors.
Maran Ha’Shulchan Aruch (Chapter 337) quotes the words of the Rambam. Thus, Hagaon Rabbeinu Ben Zion Abba Shaul zt”l rules (in his Or Le’Zion, Volume 2, page 275) that according to Maran Ha’Shulchan Aruch, one may not wash the entire house on Shabbat. However, he writes that if the floors of the house become especially soiled on Shabbat, there is room to allow washing it with water on Shabbat since this is necessary, just as our Sages allowed sweeping the floors on Shabbat.
We have heard from the great Rishon Le’Zion, Hagaon Rabbeinu Yitzchak Yosef Shlit”a, that when he was growing up, he remembers that in Maran zt”l’s home, when they had many guests on Shabbat and the floor would become especially dirty, Maran zt”l allowed the Rabbanit to mop the floor with water and a “sponga” (squeegee) stick (as opposed to with a mop or anything else that is absorbent and squeezable).
Thus, halachically speaking, the floors of the house should not be washed on Shabbat. However, if the floor becomes especially dirty locally, such as if juice or gravy spilled in a specific location, it is then permissible to pour water there and wipe it away in a way that will not cause any concerns of squeezing on Shabbat, such as with a squeegee stick which is made completely of rubber.