Potassium is a mineral that serves as an electrolyte in the body. It also regulates blood pressure and kidney function. You need potassium for your heart, brain, and nervous system to work properly. The balance of sodium to potassium in the body is critical for several processes. Most people in the U.S. get too much sodium and not enough potassium in their diets. Potatoes, prunes, sweet potatoes, carrots, bananas, green leafy vegetables, cantaloupe, and tomatoes are good sources of potassium. Adults should aim to get about 4,700 milligrams of potassium in their diets daily.