Answer:
Generally speaking, water is good at dissolving ions and polar molecules, but poor at dissolving nonpolar molecules. (A polar molecule is one that's neutral, or uncharged, but has an asymmetric internal distribution of charge, leading to partially positive and partially negative regions.)
Water's polarity allows it to dissolve other polar substances very easily. When a polar substance is put in water, the positive ends of its molecules are attracted to the negative ends of the water molecules, and vice versa.