The salt has something to do with reverse osmosis... You can read up on it
here. If you are using tap water to water house plants, the chlorine and such can build up in the soil, so every year or so you should really water those plants well, letting the hose run on them until they have a good chance to flush out all the built up chlorine. If I remember correctly, it's once a year for 10 minutes... I think a good rain outside would do the same.