A method for preparing a water-soluble polyamide, includes copolymerizing reactive monomers including caprolactam; ethylene glycol bis(2-aminoethyl)ether or ethylene glycol bis(3-aminopropyl)ether; and 5-sulfoisophthalic acid monosodium salt, wherein a molar ratio of caprolactam:ethylene glycol bis(2-aminoethyl)ether or ethylene glycol bis(3 -aminopropyl)ether:5-sulfoisophthalic acid monosodium salt is about 0:1:1 to about 5:1:1, advantageously about 1.85:1:1. Copolymerizing takes place at a copolymerization temperature of about 222-250° C. and a copolymerization pressure of about 3 Bar. The method further includes maintaining a temperature of about 222-250° C. for about 2-3 hours under normal pressure after the copolymerization step. The water-soluble polyamide has a solubility in water of about 10-70%.