The campaign, running on several television stations, uses humor to persuade people to reduce flushes, according to Brazilian environmental group SOS Mata Atlantica.
If a household avoids one flush a day, it can save up to 4,380 liters (1,157 gallons) of water annually, the group said.
The ad is "a way to be playful about a serious subject," said SOS spokeswoman Adriana Kfouri.
The spot features cartoon drawings of people from all walks of life -- a trapeze artist, a basketball player, even an alien -- urinating in the shower.
Narrated by children's voices, the ad ends with: "Pee in the shower! Save the Atlantic rainforest!"