We recommend using minimal amount of water if you decide to use water in your glass attachment. Using a minimal amount of water helps to ensure water will not enter the enail attachment thus avoiding any issues damaging your product.
Look carefully at the base of the bubbler attachment's arm. You should see two percolator slits in the column inside the bubbler. Use this as your fill line, and fill with water to just above these slits for the perfect amount of filtration, without risking water splashing your lips or damaging the heating element.