Brazilian environmental group SOS Mata Atlantica says the campaign, running on several television stations, uses humor to persuade people to reduce flushes.
The group says if a household avoids one flush a day, it can save up to 4,380 liters (1,157 gallons) of water annually.
SOS spokeswoman Adriana Kfouri said Tuesday that the ad is "a way to be playful about a serious subject."
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!"