instruction: How do you clear a scuba mask underwater ?
response: If your scuba mask fills with water while you are submerged, you can clear the water by following this simple process.
  
  1) Inhale through your mouth
  2) Push the top front edge of the mask towards your face, or lightly lift the lower section from your face
  3) Exhale through your nose.
  
  By reducing the pressure on the lower portion of the mask, and exhaling through your nose, the air added to the mask will force the water out of the bottom seal.