Which of the following materials is not considered a high hazard?

Water is not considered a high hazard material because it is typically viewed as a safe and essential substance for human health and the environment when it is free from contaminants. In the context of backflow prevention and public health, high hazard materials are those that pose significant health risks if they were to enter the potable water supply.

Raw sewage, caustic soda, and radioactive waste are categorized as high hazard because their introduction into drinking water can lead to serious health consequences. Raw sewage contains numerous pathogens that can cause disease, caustic soda is a strong base that can cause chemical burns and other health issues, and radioactive waste poses risks associated with radiation exposure.

Thus, water, when uncontaminated, is considered safe and does not fall into the same hazard category as the other materials listed.