Substances that are attracted to water molecules are known as hydrophilic molecules. These molecules can interact on a molecular level with water and are also known as water soluble molecules.
Conversely, there are molecules that are not attracted to water at all. These molecules are known as hydrophobic molecules. They cannot form hydrogen bonds and are completely insoluble in water. Hydrophobic molecules are also non-polar, while hydrophilic molecules are always polar. Molecules can be either hydrophobic or hydrophilic based on their atomic arrangement and their polarity. These two classifications of molecules are important in biological processes, since the human body has both hydrophobic and hydrophilic areas.