Catabolic and Anabolic Reactions
Starting of with the basics, reactions are the breaking of bonds in the reactants and the forming of bonds in the products.

To answer your questions about water, there is not always H2O present, although most of the times there is water. You are referring to the hydrolysis and dehydration synthesis reactions, in which water is added or removed, to break down and combine molecules, respectively. 

Catabolic reactions are more defined as the net release of energy in the reaction. They break down bigger molecules to smaller molecules. There is a need for energy input to begin the reaction and break the bonds of the reactants, however, the release of energy when the bonds of the products form are far greater, resulting in a net release of energy.

Anabolic reactions are essentially the opposite, where smaller molecules are combined and built up to larger macromolecules, many times with the removal of H2O. This results in a net decrease in free energy, as energy is absorbed/stored in the larger molecule. Energy inputted to break bonds of the reactants are far greater than the small energy released as bonds form.

As you will learn soon, these reactions can be characterized by exergonic/exothermic, and endergonic/endothermic reactions. They can be considered synonymous in many cases.