Water lock on Apple Watch serves two purposes:
- Lock the touchscreen so the water doesn't accidentally "tap" on a button or notification.
- Expel water from the speaker when it's turned off.
MySwimPro automatically enables water lock at the start of a swim workout. Once it's off, you can enable it again by using the force touch menu to select Lock.
Apple Watch Series 2 and later is water resistant to 50 meters whether or not the water lock is on. It is not required that water lock is on during your swim, but we do suggest it so a notification isn't accidentally tapped on by the water. If you do choose to turn it off during your workout, we recommend you enable and disable it again after your workout to properly expel the water from the speaker.
You can learn more about the Apple Watch's water resistance on Apple's website here.