The antonyms for the phrase "becomes contaminated" may vary based on its context. However, some possible antonyms include purified, cleansed, sanitized, disinfected, sterilized, and decontaminated. These words imply that a substance or an area has been treated to remove all impurities, dirt, bacteria, or viruses, making it safe for use or consumption. For example, a water treatment plant uses various processes to purify water and remove harmful chemicals and microorganisms. Similarly, doctors and nurses follow strict sterilization procedures to prevent infections in hospitals. Therefore, using the opposite words of "becomes contaminated" can convey a positive connotation, indicating that something has been cleaned or made safe.