You can mark races Wet or Dry. Results scored with the race marked Wet will have W next to the time.
When you publish Live HTML the Graphics for the Race conditions can be set to display Wet or Dry. This is most useful when Webcasting meetings.
When you have a wet/dry meeting, if not all competitors have had a Dry qualifying race, you can set "Score Wet Heats Only" in Select Meeting to discard the Dry results.