Sha’ar HaMayim HaKatzar is the Rashba’s abridgement of his Sha’ar HaMayim HaArokh, a compilation of laws about the mikvah (ritual bath). Sha’ar HaMayim HaArokh presents rulings, explanation, and analysis of topics like valid sources of water for a mikvah and conditions that disqualify a mikvah. Sha’ar HaMayim HaKatzar presents only the actual laws. These works are found in the back of some manuscripts of the Rashba’s Torat haBayit and are quoted by commentators like the Rivash, the Tashbetz and the Beit Yosef.