I saw this during a Gatorade G2 television commercial.

Problem:
A hyphen is missing.

Explanation:
When an adjective plus a noun modify another noun, the adjective and first noun must be joined with a hyphen to form the modifier of the second noun.

So the adjective “LOW” plus the first noun “CALORIE” must be joined with a hyphen to form the modifier of the second noun “HYDRATOR”.

Unfortunately, many advertising copywriters believe that it is appropriate to drop required hyphens in their advertising copy. I disagree.

Although this is not the best example, there are many examples where the absence of a required hyphen leads to confusion and double- or triple-pass reading of copy to understand what the copywriter meant.

Solution:
“LOW-CALORIE HYDRATOR”