While an undyed, unbleached organic cotton T-shirt is the absolute greenest tee to buy, it isn't always the easiest to find. Instead, do the next best thing: Choose white T-shirts rather colored shirts. A typical T-shirt requires about 6.6 gallons of water to dye and process from white to a color. Choosing a conventional white T-shirt saves water, reduces chemical dyes and saves energy. If everyone did this, we'd save billions of gallons of water.