It is not that the waterproof band-aid can be in contact with water for a long time. If the band-aid does not stick tightly to the skin around the wound, especially in special areas such as fingertips, knees and elbows, the waterproofing will not become "waterproof".
The correct approach: When using waterproof band-aids, try to minimize contact with water, pay attention to observe and protect the wound, and promptly replace the water-soaked band-aid.