Water-sealing sheet

A water-sealing sheet comprising a water-swelling resin obtained by kneading together 10 to 97% by weight of a non-water-swelling thermoplastic resin, preferably vinyl chloride resin, containing 80 to 200 parts by weight of a plasticizer based on 100 parts by weight of the non-waterswelling thermoplastic resin, and 3 to 90% by weight of a water-swelling urethane resin. The urethane resin is a prepolymer having isocyanate groups in which the content of terminal NCO groups amounts to 1 to 12%, preferably 2 to 7%, obtained by the reaction of polyisocyanate with at least one polyether polyol of the formula R[(OR1)n OH]p wherein R is a polyhydric alcohol residue; (OR1)n is a polyoxyalkylene chain comprising oxyalkylene groups each having an oxyethylene group and an alkylene group carrying three or four carbon atoms, and wherein the content of the oxyethylene groups is 20 to 100% of the total molecular weight; n is a number corresponding to the degree of polymerization of the oxyalkylene groups and giving a hydroxyl group equivalent of 200 to 2500; and p is 2 to 8, preferably 2 to 4.