A solution with a salt-sensitive polymer binder for use in fibrous webs, where the binder contains a copolymer of carboxylic acid monomer units and ethylenically unsaturated monomer units. The binder solution is prepared by emulsion-polymerizing a copolymer and then neutralizing the copolymer with base to make it water soluble. The binders provide a higher wet strength in concentrated salt solutions than in deionized water, and are particularly suitable for strengthening nonwoven fibrous webs in disposable articles such as wet-wipes, personal care products, diapers, and the like.