A composition for treating a portion of a wellbore or a portion of a subterranean formation is provided, the composition comprising: (a) water; (b) a source of hydrogen peroxide, and (c) an activator for the source of hydrogen peroxide; wherein the pH of the composition is adjusted to be within an appropriate range for the type of activator. A method for treating a portion of a wellbore or a portion of a subterranean formation, the method comprising the steps of: forming or providing a composition comprising: (a) water; (b) a source of hydrogen peroxide, and (c) an activator for the source of hydrogen peroxide; wherein the pH of the composition is adjusted within an appropriate range for the type of activator; and introducing the composition through a wellbore to treat a portion of a wellbore or a portion of a subterranean formation. The activator can be a water-soluble alkanoyl-donor compound or a chelated transition metal. Preferably, the composition further comprises an iron chelating agent. The composition and method are adapted for breaking a viscosity increasing polymer, such as xanthan. The method has particular applications where the static temperature of the portion of the wellbore or the portion of the subterranean formation to be treated is less than 100° F. (38° C.).