Imagine a box that’s half-filled with 15 blue marbles. If that box could be divided into 5 parts and all the parts would have the same number of marbles, you’d get 3 marbles in each box part. That’s the “density”; the number of marbles per box part.

Now imagine that same whole box, and you add 5 white marbles. This would be the salt, which would make the water saline. You’d have a total of 20 marbles now, of blue and white mixed together. If you divided that box into 5 again, each part would have 4 marbles, 3 blue ones and 1 white one. Since this one has more marbles for each box part (4) than the first one (3), we can say that the second one is DENSER. Salinity adds to mass (no. of marbles) but not to the volume (size of box). Thus, the more salinity, the denser.

Temperature may also affect water density. When the temperature is high, molecules in water disperse and move around more rapidy than they usually do in order to spread the heat energy. But when the temperature is low, water molecules move less and lose energy, and because of this, the space that they move in becomes smaller. Since there is less space and yet the same number of molecules, the density increases. This is why coffee is less hot at the bottom than at the top; the less hot molecules of the coffee are heavier than the hotter ones, and they settle at the bottom.

In summary: Colder temperature=more density

Higher temperature=less density

Higher salinity=more density