My daughter has been diagnosed non-salt-wasting; however, the dr agrees she is probably a very slight salt waster.  Heat is her biggest stressor. We watch her carefully in sports, but she still rides horses, plays softball and basketball (though we had to stop basketball this winter because the coach practiced them too hard and she could not handle it - getting overheated, etc.  I didn't want to stress dose her after every practice!)  We have even experienced problems when we went to a theme park for the day and the temps hit in the 90's - all that concrete and the heat reflecting off it.  We have learned to watch her carefully, give her Gatorade and salty snacks, and if we know ahead of time it will be a problem, we give her an extra dose of her hydrocortison before she is in the heat.  She is almost 13 now and recognizes symptoms and will tell the coach she needs a break or take herself out of a game if necessary.  It works.  Please, everyone, be careful in the summer heat.  I hope your kids all have a healthy and fun summer vacation.