Excerpt from Valley 101: A Slightly Skewed Guide to Living in Arizona, a collection of Clay Thompson’s columns for The Arizona Republic. (Originally published August 17, 2001.)
Q: We are recent transplants to Arizona from Washington, where it rains a lot, so we never had to worry about this before: Can you get sunburned under the water?
A: I will answer that in a moment, but first I need to remind you that as new Arizonans and pool owners, it is your duty to sit by the pool on Thanksgiving Day and call relatives in colder climates and say, “Hey, guess what we’re doing?”
As you no doubt know, it is the ultraviolet rays in sunshine that cause sunburn. Clouds or fog or water block out some of those rays, but still up to 70 or 80 percent beam through.
One source I found said ultraviolet rays can penetrate clear water to a depth of 25 centimeters, and of course 25 centimeters is the same as 9.85 miles.Wait, that can’t be right. Inches, it’s the same as 9.85 inches.
There is also the question of reflection. If you’re bobbing in the pool with sunscreen smeared all over your bald spot, you can still end up sunburned because some of the ultraviolet rays are bouncing off the water and smacking you in the face.
There are a number of precautions you might take. First, you could keep rotting vegetation in your pool to cloud the water. This would be yucky, but it would keep harmful rays from penetrating as deeply as they would in clear water.
Or you could swim fully clothed, including a hat and gloves. This might be better than the rotting vegetation idea.
Or, and this might be best, you could coat yourself with the best, water-resistant sunscreen you can find. Get one with an SPF of 15 or higher and make sure the label says it protects from both UVA and UVB, which are the two bands of ultraviolet light that burn us.
And don’t forget about that Thanksgiving thing. Mark it on your calendar now.