The low or high salt content of water should have no effect at all on the way the Steripen works.

The salt content will effect the electrical conductivity (EC) of the water and can also have an effect on the taste. UV treatment does not require any level of EC to work; it does require clear water.

If the salt content is too high, alkaline for example, the water will have a bitter taste and can give one a fair case of the "green apple quickstep". If the wrong salts are present (eg. arsenic, selenium) the water can be poisonous.
May I walk in beauty.