Methods for the use of peracid compositions having decreased hydrogen peroxide concentration and a UV-blocking agent for various water treatments, including oil- and gas-field operations, and/or other aseptic treatments are disclosed. In numerous aspects, peracetic acid is the preferred peracid and is treated with a peroxide-reducing agent to substantially reduce the hydrogen peroxide content. Methods for using the treated peracid compositions for treatment of drilling fluids, frac fluids, flow back waters and disposal waters are also disclosed for improving water condition, reducing oxidizing damage associated with hydrogen peroxide and/or reducing bacteria infestation.