What is the purpose of immersing hermetically sealed equipment in freshwater?

Immersing hermetically sealed equipment in freshwater serves the specific purpose of testing the air-tight integrity of the seal. By submerging the equipment, any potential leaks in the hermetic seal can be detected. If the seal is compromised, water will enter the equipment, indicating that the integrity has been breached; this is crucial for ensuring the reliability and functionality of the equipment, especially in sensitive avionics applications where moisture intrusion can lead to significant malfunctions or failure.

While cleaning (the first option) or removing contaminants may seem like logical alternatives, these processes would not specifically evaluate the air-tightness of the seal. Lowering temperature, another option, does not relate to the seal integrity, as temperature changes are not a method for assessing whether a hermetic seal can maintain its function and prevent ingress of moisture. Thus, testing the air-tight integrity through submersion in freshwater is a focused and effective technique for confirming that the hermetic seal is intact.