Disclosed is a macromolecular water-treatment membrane that provides improved water-treatment efficiency while also exhibiting good mechanical strength, water permeability, and the like. Also disclosed is a manufacturing method that can easily and reliably manufacture macromolecular water-treatment membranes. Further disclosed is a water treatment method capable of efficient water treatment/maintenance. The disclosed macromolecular water-treatment membrane comprises hollow-fiber membranes with a free-standing structure due to a roughly uniform principal constituent material that has outer diameters between 3.6 and 10 mm and SDR values (the ratio between outer diameter and wall thickness) between 3.6 and 34. In the disclosed manufacturing method, a macromolecular water-treatment membrane is manufactured by: preparing a resin solution from a roughly uniform material; pouring the resin solution, at an angle of at most +-30 DEG from the horizontal, from a spout into a solidification tank; and solidifying the resin solution. In the disclosed water-treatment method, either the disclosed macromolecular water-treatment membrane is used as a separation membrane, or wastewater that has been biotreated by activated sludge is run through the interior of the disclosed macromolecular water-treatment membrane in order to separate out water.