Sodium is necessary for your metabolism - it is critical to nerve function in the proper concentration. Excess sodium, however, is not good.
Ion exchange water softeners do add sodium (some can use potassium) ions to the water - its how they work. Its why water softeners are not recommended for people with heart conditions. The calcium and magnesium ions in the water (which are a problem for plumbing and interfere with the sudsing action of soap) are exchanged for sodium ions on the surface of the resin beads. The resin beads prefer to hold calcium or magnesium ions over sodium so that's how the chemistry happens. When regenerating, a strong concentration of sodium chloride solution drives the reaction backward but the excess sodium chloride (plus the now calcium or magnesium chloride) is flushed to the drain before you could get that into your plumbing thanks to the automatic bypass valve.
I always remember a few years ago when a group I belong to had a presentation from a member who was a certified hazardous chemicals in agriculture instructor. He was telling us the meaning of LD50 (the lethal dose in 50% of test subjects). An example he used was that, given a cup of Roundup and a cup of salt, which would you choose to consume? Given the hysteria around pesticides (not even herbicides like Roundup - they are often wrongly grouped together) most people would choose the salt - and be dead. Only the people who knew a little biochemistry (and that they are not plant-based) would correctly choose the Roundup.
2015 Rockwood Signature UltraLite 8282WS Platinum, GY Marathon LRD, TST 507RV TPMS
2005 GMC 2500HD CCSB D/A, Curt E16, Prodigy P2, Garmin RV760LMT w/BC-20 b/u cam
Self restraint is for the young. I'm old and want it NOW!