The sweating process begins in the hypothalamus in the brain. This sensitive gland knows when the body's core temperature rises, and it sends out the signal to other glands to start sweating. By drinking cool water, however, you can short circuit this cycle. Staying hydrated will keep the body's internal temperature lower, reducing the call for sweat production. You should drink as much water throughout the day as it takes to prevent thirst (a sign you're already dehydrated) and keep your urine more clear than yellow. Which means that you'll need to increase your usual amount of water intake under certain circumstances, like hot weather or rigorous exercise [source: Vella].
If you know you'll be in a sweat-prone environment, you can also boost your antiperspirant by applying talcum power or baking soda to your underarms to soak up moisture and prevent odor.
You can also turn to a common fruit to help control underarm sweat. While limes are a common ingredient in many cuisines (do margaritas count as a cuisine?), they may reduce sweating, too. Before going to bed, cut a lime in half and rub it under your arms until the skin is coated in juice, then let it dry. The citrus will work as a natural deodorant, and the acidic juice may help stop sweat from being produced [source: Bassitt].