Provided are a method for producing a water-soluble polymer in which a water-soluble polymer can be produced from a pressure-sensitive adhesive as waste under a mild condition, a method for producing a water-absorbent polymer in which a water-absorbent polymer can be produced from a pressure-sensitive adhesive under a mild condition, a water-soluble polymer that can be produced from a pressure-sensitive adhesive, and a water-absorbent polymer that can be produced from a pressure-sensitive adhesive. A method for producing a water-soluble polymer according to an embodiment of the present invention includes bringing a pressure-sensitive adhesive treatment liquid which contains a liquid having a Hansen solubility parameter value of 31 or less and an alkaline compound and in which a concentration of the alkaline compound in the pressure-sensitive adhesive treatment liquid is from 0.001 wt% to 20 wt%, into contact with a pressure-sensitive adhesive.