A water tank for an aircraft, comprising: a tank main body including a cylinder and domes disposed at both ends of the cylinder; and a tank port disposed on the cylinder; the cylinder including a cylindrical inner liner, a plurality of fiber-reinforced resin layers disposed on an outer peripheral surface of the inner liner, and a core layer disposed between the fiber-reinforced resin layers; the cylinder including a through-hole extending through the cylinder; and the tank port including: an inner member including an inner cylindrical portion inserted into the through-hole and protruding from an outer peripheral surface of the cylinder and an inner fitting plate portion expanding outward in a radial direction from a base end of the inner cylindrical portion protruding from an inner peripheral surface of the cylinder over an entire periphery of the inner cylindrical portion, the inner fitting plate portion being attached around the through-hole on the inner peripheral surface of the cylinder; a reinforcing sheet including an opening for inserting the inner cylindrical portion protruding from the outer peripheral surface of the cylinder, the reinforcing sheet being attached to a region, corresponding to an entire periphery of the through-hole, of the outer peripheral surface of the cylinder, the reinforcing sheet reinforcing the region of the outer peripheral surface; and an outer member including an outer cylindrical portion attached to an outer peripheral surface of the inner cylindrical portion protruding from the opening and an outer fitting plate portion expanding outward in a radial direction from a base end of the outer cylindrical portion over an entire periphery of the outer cylindrical portion, the outer fitting plate portion attached to the reinforcing sheet. a tank main body including a cylinder and domes disposed at both ends of the cylinder; and a tank port disposed on the cylinder; the cylinder including a cylindrical inner liner, a plurality of fiber-reinforced resin layers disposed on an outer peripheral surface of the inner liner, and a core layer disposed between the fiber-reinforced resin layers; the cylinder including a through-hole extending through the cylinder; and the tank port including: an inner member including an inner cylindrical portion inserted into the through-hole and protruding from an outer peripheral surface of the cylinder and an inner fitting plate portion expanding outward in a radial direction from a base end of the inner cylindrical portion protruding from an inner peripheral surface of the cylinder over an entire periphery of the inner cylindrical portion, the inner fitting plate portion being attached around the through-hole on the inner peripheral surface of the cylinder; a reinforcing sheet including an opening for inserting the inner cylindrical portion protruding from the outer peripheral surface of the cylinder, the reinforcing sheet being attached to a region, corresponding to an entire periphery of the through-hole, of the outer peripheral surface of the cylinder, the reinforcing sheet reinforcing the region of the outer peripheral surface; and an outer member including an outer cylindrical portion attached to an outer peripheral surface of the inner cylindrical portion protruding from the opening and an outer fitting plate portion expanding outward in a radial direction from a base end of the outer cylindrical portion over an entire periphery of the outer cylindrical portion, the outer fitting plate portion attached to the reinforcing sheet.