In a large bowl, combine the water, buttermilk, egg and oil; mix well and set aside.
In a separate bowl, add brown rice flour, potato starch, tapioca flour, xanthan gum, salt, sugar, egg replacer (optional) and yeast. Whisk to combine.
With the hand mixer on a low speed, gradually add the flour mixture to the water mixture; mix until well blended. Beat about 10 minutes. Pour batter into three 2x5-inch greased bread pans or one large 9x5-inch loaf pan. Cover; let rise approximately 1 hour.
Preheat oven to 375°F.
Bake for 30 minutes for 3 small pans or 60 minutes for 1 large pan. Use a toothpick to test for doneness.
When baking is complete, remove the pan from the oven and wait for 10 minutes before removing the bread from the pan. Cool on wire rack before slicing.