Excellent question! Liquid water is an amazing fluid— it is possibly the most relevant molecule that keeps us and most living things on Earth alive.

One important property of water is that it can hold other molecules or ions (charged particles). Salt, for instance, is made of two ions called sodium (Na+) and chloride (Cl-). When salt is put in water, the water itself will actually seem to absorb the ions because it is attracted to these charges. Pure water can hold large amount of salt without changing its volume very much— in fact, for every 1 pound of water, you could hold over 1/3 pound of salt in it!

The key concept here is that the density of water changes when you add salt. Density is measured by taking the weight of the liquid divided by its volume. Adding salt will gradually increase the water’s density. You can prove this by dropping something like a carrot slice into pure water—observe that it should sink to the bottom because carrot is denser than regular water. But by adding salt to the water, eventually you will see the carrot float up to the top! This is because the water density is slowly increasing and eventually becomes denser than the carrot.