Q. I’m about to take a snorkeling vacation. What sunscreen will protect me best while I’m in the water?

A. Water resistant sunscreens are required by the Food and Drug Administration to meet the SPF listed on their labels for the amount of time they claim to be water resistant, but our tests have shown that not all do.

One product in our latest tests, Shiseido WetForce Ultimate Sun Protection Lotion SPF 50+ ($40 for 3.3 ounces, or $12.12 per ounce), makes a very specific claim: being in the water for 30 minutes actually boosts its ultraviolet (UV) protection by 20 percent. But we found that although it met its SPF claim and provided Excellent protection against UVB rays (those that cause sunburn), its average SPF was the same whether testers’ skin was dry or exposed to water for 30 minutes. And because of its performance in our UVA test (UVA rays cause skin cancer and wrinkles) and other factors, it earned only a Fair rating overall.

We found other water resistant sunscreens that cost less and earned Excellent ratings for UVA and UVB protection: Coppertone Water Babies SPF 50 ($10.50 for 8 ounces, or $1.31 per ounce) and Walmart’s Equate Ultra Protection SPF 50 ($9 for 16 ounces, or $0.56 per ounce).

For more, check our Sunscreen Buying Guide and Ratings.

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Editor's Note: This article also appeared in the January 2016 issue of Consumer Reports magazine.