The ocean is a comfortable 80 degrees Fahrenheit in Mexico where I guide and teach diving. The air, however, is frequently much, much warmer. Divers travel to tropical beaches to experience coral reefs that thrive in warm waters - the hot climate is part of the lure. Yet, many divers forget that the strong sun and high humidity of many dive destinations can quickly dehydrate. Add to this the tendency of many divers to consume above average quantities of margaritas and beer while vacationing, and the potential for dangerous dehydration becomes apparent.
I try to encourage my divers to drink water as much as possible. Before beginning one of my rather zealous dive briefings about the spectacular aquatic life and submarine environment of the Riviera Maya, I distribute water to every one of my clients. I also hand out water after the dives. Few people actually drink the water. Perhaps they are afraid of peeing in their wetsuits or perhaps they simply don't feel thirsty. Most people are not accustomed to drinking the large quantities of water necessary to maintain proper hydration for multiple dives in a hot environment.
Why is staying hydrated so important? In a warm environment, divers sweat more than normal. When they breathe dry air from a scuba tank, divers lose even more water. Dehydration can lead to headaches (who wants a headache on vacation?) and general exhaustion. Most importantly, dehydration is one of the leading factors that predisposes a diver to decompression sickness. Dehydration is not only uncomfortable, it can actually be dangerous!
I am constantly encouraging divers to drink more hydrating liquids. If you, like many divers, find consuming adequate quantities of water difficult, a good solution is to bring yummy, non-alcholic, caffeine-free beverages along for the trip. Store them in the boat or dive guide's cooler. Fresh juices, chocolate milk, and packets of powered drink mix all work well. I love the single-serving packets of Crystal Light® that can be mixed directly into a bottle of water. For serious hydration, skip Gatorade which contains high amounts of potassium that your body will not use when scuba diving, and go for hydrating fluids such as Pedialyte. Pedialyte can actually be palatable when mixed with water and consumed well-chilled. Beverages that are not great for hydration include coffee (even though I love it), sodas, and margaritas (sorry).
Also remember that while drinking liquids immediately before and after a dive will help a diver's body to hydrate, it can only do so much. A diver who is habitually dehydrated will not be able to solve the problem by chugging water only when diving, because the body can only absorb so much water at a time. To function at its best, a diver's body needs to be in a well-hydrated state, have additional fluids available to maintain hydration while diving, and have even more water to replenish itself after a dive. This means that divers should strive to maintain hydration during their entire diving vacation, not only before and after a dive. This is also one of the many reasons that it is an extremely bad idea to dive hung-over.
The very sport that immerses us completely in water also causes us to lose it. I try to convey this concept to students and certified divers alike. Still, after several dives, I usually end up with hot, dry-mouthed, and exhausted divers who just want a nice, cold beer.