Simulated systems are used to investigate the self-purification capacity of natural water, depending on its redox state. One-time introduction of hydrogen peroxide is shown to maintain the oxidized state of the aquatic environment for a long time, which makes its reintroduction unnecessary and ensures increased saturation of water in dissolved oxygen, virtually to the same level as could be achieved by twenty-four-hour aeration. The presence of hydrogen peroxide in the aquatic environment is found to promote more effective and profound destruction of organic matter, even under low temperature conditions, when biochemical oxidation processes are decelerated.