How to predict if a substance will dissolve in water?

Water is made out of H2O molecules. These molecules are polar. This means that the electrons move closer to the oxygen nucleus (because the oxygen nucleus is heavier). In general, water can dissolve only polar and ionic compounds. So, by taking a look at the substance's structure (using something like X-ray spectroscopy or an electron microscope), you can determine if it is polar, ionic or nonpolar substance (I won't get in much detail about the types of bonds there are), thus determining if it will disolve in water or not.