When you add salt to water the level goes down
When you add a volume of sodium chloride (salt) to a volume of water, the overall volume actually decreases by up to 2%. This is called electrostriction.
The solvent molecules become more ordered in the vicinity of dissolved (charged) ions and less ordered as we go further away from the dissolved (charged) ions. The increase of solvent density near the ions is offset by the decrease of bulk density in the solvent as distance from the ions increases. This results in an overall net reduction in the observed volume of the solution. Try it at home!