We introduced a new electret condenser Microphone (ECM) water repellent coating structure for protection against common hazards, such as water or alcohol. This protection structure is composed of small acoustical holes with a water-repellent coating. The water-repellent coating has a contact angle of more than 150 degrees for water on a small acoustical hole having less than 0.2 mm aperture, which blocks water invasion but allows acoustical transmission. The reliability of the coating was confirmed by several tests, such as long-term immersion in water and alcohol, re-flow soldering test and surface scratching. These tests produced no damage to the coating. The fabricated ECM meets the requirements for the IEC 60526 class 7, which is 30 minutes under water at a depth of 1 meter. The diameter and number of holes is determined both by acoustic characteristics and water resistance.