Mixtures are physical blends of matter, that retain their own properties.  They are mixed up, but they are not something new.

To separate mixtures, you need to take advantage of a difference in their physical properties.  

You can filter apart some mixtures, or use a magnet on other mixtures, or boil apart different liquids if you carefully heat them up just over the boiling point of one, but not the other.

Or you can use CHROMATOGRAPHY, using water to separate by both solubility in water, and by density (smaller particles of color take longer rides than the more dense particles.

Here are some cool examples of that.  There were many to choose from, this is a tiny sample of many excellent pieces of art.