Wearable electronic devices have been commonly adopted for different possible purposes, for examples, hearing aids, pacemakers, smartwatches, and other forms of health-monitoring devices carried during daily activities, exercise and water sports. Professional athletes, especially who engage in extreme sports related to water including cave diving, surfing and windsurfing, have to compete under harsh environmental conditions. With the aid of the wearable devices, they are allowed to record their sports performance more conveniently. Nonetheless, the reliability of the wearable electronic device must be enhanced so that it could function normally under different environmental situations. The most prevalent way for electronic devices to cause damage is contact with water. To design and fabricate wearable electronics, which withstand different environmental hazards, will ensure accurate and reliable health and other useful information obtained for the athletes and other device users. Therefore, reliability testing is a critical and fundamental ingredient for the design of more reliable and better wearable electronics devices. Before promotion and release to the market, the product should comfortably withstand different environmental conditions for different uses by the consumers. This paper demonstrates various forms of the experimental verifications for analyzing the waterproofness of smartwatches including printed circuit boards and electronic components under IPX7 (International Protection Marking, IEC standard 60529) testing standard conditions in tap water and salt water by considering Xiaomi Mi Band 2 as a real case. Using a modification of the IPX7 testing standard, four tests were conducted including water immersion test, with tap water and seawater, diving test and water jet test. The results on the IP67, waterproof because of adopting the airtight sealing and anti-sweat material, will be demonstrated, with fabrication method, and proposals for better design. The printed circuit board (PCB) also presented a significant increment in the amount of corrosion in solder joint due to water-induced damage . In summary, the results have clearly demonstrated the waterproof performance of the smartwatch and this is one of the crucial systematic studies of the reliability of wearable smartwatches subjected to IPX7 testing standard. The failure discussed in this paper may contribute for enhancing the design of more reliable smartwatches and wearable devices generally to avoid water-induced damage during operation and achieve a longer lifetime and accurate health data under harsh environmental conditions.