Barium hydroxide, chemically written as Ba(OH)2, is soluble in water, according to Purdue University's Bodner Research Web. Barium hydroxide is a hydroxide salt; normally these types of salts are usually insoluble in water, but barium hydroxide is an exception to the rule.
In water, barium hydroxide dissociates completely into a Ba2+ cation and an OH- anion. In chemical reactions, because barium hydroxide is completely soluble, it does not form a precipitate in water, and is able to react as an ionic solution. Solubility rules indicate which compounds are soluble in water and which are insoluble. Barium hydroxide is an exception to the solubility rules, along with NaOH, KOH, Sr(OH)2 and Ca(OH)2.