An improved system of resins comprising a combination of a sulfate-specific strongly basic anion exchange resin and a heterogenous hybrid thermally regenerable salt sorbent (TRSS) resin is provided. The anion exchange resin contains triethylamine and/or tributylamine groups. The TRSS resin comprises a macroporous host copolymer and a crosslinked guest copolymer having, respectively, weak acid groups and weak base groups. The system is used to treat feed water containing dissolved ions, including sulfate ions, and is efficiently regenerated.