In a large bowl, whisk the teff flour with the water until a smooth batter forms. Cover the bowl with plastic wrap and let stand at room temperature overnight; the batter will be slightly foamy.
Heat a 12-inch nonstick skillet over high heat. Whisk the salt into the batter. Ladle 3/4 cup of the batter into the skillet; swirl to coat the bottom with batter. Cook over moderately high heat until the injera just starts to bubble, about 30 seconds. Cover the skillet and cook for about 30 seconds longer, until the injera is cooked through and the surface is slightly glossy. Invert the skillet onto a work surface, letting the injera fall from the pan. Repeat with the remaining batter.