Since water softeners use salt to deal with hard water, the outcome is a water sample that contains a high amount of sodium (depending on the initial hardness level of water). But even at its worst state, you need not worry about the safety of drinking softened water unless of course you are following a low-sodium diet. In that case, you could use potassium chloride instead of salt in your brine solution. But do make sure you contact your softener's manufacturer before doing so.