Underwater mode is nothing else than a red filter, even with a red filter you should white balance hence the underwater mode is not an option
To set white balance the procedure is func set navigate to the customer WB and then press menu, if this is too annoying the shortcut button can be set to custom white balance
For what concerns the comment from ivakdiver, autofocus underwater is a pain and with a wide angle lens you don't actually need to refocus much anyway
To help you out look at manual page 99
Shooting with focus lock
keep the shutter button half pressed then press left arrow
The MF indicator appears and you are in focus lock
Press left and left again to release focus lock
To set white balance the procedure is func set navigate to the customer WB and then press menu, if this is too annoying the shortcut button can be set to custom white balance
For what concerns the comment from ivakdiver, autofocus underwater is a pain and with a wide angle lens you don't actually need to refocus much anyway
To help you out look at manual page 99
Shooting with focus lock
keep the shutter button half pressed then press left arrow
The MF indicator appears and you are in focus lock
Press left and left again to release focus lock