Some facts about the Sun:

• sitting in the shade does not protect you from the sun - only 20% of UV light is reduced this way
• did you know that up to 80% of sun's rays get through:
  • fog
  • mist
  • light clouds 
• when your shadow is the shortest, the sun's rays are the strongest 
• water reflects about 80% of UV rays
  • you get UV exposure from two directions, namely:
    • directly from the sun and indirectly from the UV light reflected back from the water 
  • reason for more severe sunburns when you are in or near water
• water-proof sun screens / blocks and protectants -
  • there are no such things, they do not exist - they are marketing hype
  • the best you can achieve is water-resistant - which means they resist, to a certain degree, the water, but will come off when swimming, washing or sweating heavily