“Iroh: “Euch! This tea is nothing more than hot leaf juice!”
Zuko: “Uncle, that’s what all tea is.”
Iroh: “How could a member of my own family say something so horrible?’’”
— Iroh and Zuko in City of Walls and Secrets.

Iroh serving tea.

Tea is the most commonly served beverage in the World of Avatar. It is made from a variety of leaves and herbs, which are immersed in hot water and drank immediately. No additives, such as milk or sugar, are added to the brew.
Almost every person in the world has drank tea at some point, due to its availability. Though relatively common, tea is not actively drank in the Water Tribes.

Varieties

Chi-Enhancement
Chi-Enhancing Tea is a natural stimulant. When drank by members of the military, it improves strength and increases energy ten-fold.

Ginger
An herbal concoction, Ginger Tea is made through the use of ginger roots. It is primarily used as medicine.

Ginseng
Ginseng is a very delicious tea favored in The Land of Fire

Green
Green tea is primarily enjoyed by the populous of The Land of Earth

Jasmine
Said to be a relatively soothing brew, Jasmine Tea is a favorite of Iroh.

Lychee
This brew is vastly enjoyed by the citizens of Ba Sing Se. It can be assumed this tea is made from Leechi Nuts, and as such, is commonly found in many parts of the globe, due to the fruit’s availability.

White Jade
A tea made from the White Jade Bush which is poisonous.

Spiced Tea
A spiced tea commonly served in The Land of Fire.

White Dragon
The White Dragon produces tea that Iroh describes as, “so delicious, it’s heartbreaking.” Apparently, it is often confused with the poisonous White Jade, due to the plants’ similar appearances and coloration. A delicacy to citizens of the Dragons of the White Lotus