Water dissolves so many substances because its polarity lets it surround and separate charged particles:

• Ionic compounds like salt dissolve because water molecules surround each Na+ and Cl- ion, pulling them apart from the crystal
• Polar molecules like sugar dissolve because water's hydrogen bonds interact with the molecule's own polar groups
• Nonpolar substances like oil do not dissolve because they cannot interact with water's charges — this is the basis of the "like dissolves like" rule
• This dissolving power makes water essential for biological chemistry — nearly every reaction in your body happens in aqueous solution.