For the past two years, Crystal Light under new agency McGarryBowen has been making a simple, straightforward and fairly serious pitch: "Your body needs water. And women who drink Crystal Light drink 20% more of it."

But the brand's sales have been watered down of late. For the year ending Nov. 27, sales fell nearly 8%, to $170 million, in the $600 million-plus fruit-drink-mix category, according to SymphonyIRI, which tracks grocery sales, excluding Walmart Stores. Now Kraft Foods is pulling the plug on the "Water Your Body" campaign, replacing it with a sassier, more humorous effort as it seeks to reinvigorate the 30-year-old brand.

The new tagline, called "Stay Light," will be pushed with TV, print and digital ads as well as events. Kraft plans to increase spending on the brand by 40%. Crystal Light got about $46 million in measured-media support in 2010 and $37 million in the first 10 months of 2011, according to Kantar Media.

"As we were talking to our consumers, what really came out is that these people want to celebrate, want to feel good," said Crystal Light Brand Manager Josh Kroo. "We can help them embrace the lighter side of their struggles that they have with weight and their body image." The brand stands behind its water message but wanted to move on from the "very serious tone" to a more emotional appeal, adding a "sassy, clever voice in our advertising," Mr. Kroo added.

Crystal Light is also introducing innovations, including energy-drink versions that contain 60mg of caffeine per 8-ounce serving and "energy-releasing B vitamins."

Here is the new TV ad. It launches Jan. 2 on major broadcast networks and cable outlets, including Lifetime, Bravo and OWN.