Bring the brown rice and water to a boil in a saucepan. Reduce heat to medium-low; cover the saucepan and simmer until the rice is tender and the liquid has been absorbed, 45 to 50 minutes. Allow the rice to cool.
Place the rice, endive, and red onion in a large bowl. Drizzle the balsamic vinegar and olive oil on top, and season with salt and pepper. Mix thoroughly.