How can I tell if my sourdough starter is ready to use (gluten only)?

To determine if your sourdough is active and ready to use, drop a small amount (about ½ tsp) in a small bowl of cool water. If the starter floats at the surface, it is ready to use. If it sinks or floats under the surface of the water, the starter needs more time sitting at room temperature to activate, or it needs more flour and water as fuel.