That water is heated in a detachable reservoir that doubles as a kettle. This is a unique feature for a coffee maker, but one we ended up appreciating, especially for households with a mix of tea lovers and instant-oatmeal eaters alongside coffee drinkers. Fill the kettle up, lock it in place, and scroll the dial to the amount of coffee you want brewed. The machine is designed so that, even if you have more water in the kettle than you need, it will brew only the amount you specify. The one thing you actually have to measure with the OXO On 12-Cup is the grounds. Do that right, and it’s pretty much impossible to screw it up.
Bunn-O-Matic came out with a different drip-brew machine. In this type of coffeemaker, the machine uses a holding tank or boiler pre-filled with water. When the machine is turned on, all of the water in the holding tank is brought to near boiling point (approximately 200–207 °F or 93–97 °C) using a thermostatically-controlled heating element. When water is poured into a top-mounted tray, it descends into a funnel and tube which delivers the cold water to the bottom of the boiler. The less-dense hot water in the boiler is displaced out of the tank and into a tube leading to the spray head, where it drips into a brew basket containing the ground coffee. The pourover, water displacement method of coffeemaking tends to produce brewed coffee at a much faster rate than standard drip designs. Its primary disadvantage is increased electricity consumption in order to preheat the water in the boiler. Additionally, the water displacement method is most efficient when used to brew coffee at the machine's maximum or near-maximum capacity, as typically found in restaurant or office usage. In 1963, Bunn introduced the first automatic coffee brewer, which connected to a waterline for an automatic water feed.