Combine the amaranth and water in a medium saucepan. For thicker consistency, use about 2 1/2 cups of water; for a softer, goopier texture ideal for porridge, use closer to 3 cups of water.
Bring to a boil over medium-heat, then reduce to low and simmer.
Cook for about 30 minutes, or until the water is absorbed, stirring occasionally. The amaranth should be soft, with a creamy texture.
Remove from heat and let sit for a few minutes to allow any remaining water to fully absorb.
Season and customize by stirring in fresh herbs like parsley, a sprinkle of chopped nuts like almonds, your favorite spices, or a bit of lemon zest for brightness.