Adding water to a substance can be done in several ways. Thinning is the process of reducing the viscosity of a liquid by adding water, which is done by using the four letter word 'THIN'. Diluting is the process of reducing the concentration of a solute in a solution by adding more solvent, which is done by using the six letter word 'DILUTE'. Hydrating is the process of adding water molecules to a substance, which is done by using the seven letter word 'hydrate'.