Water plays a critical role in preparing grains and starches like pasta, couscous, rice, and hot cereals. When cooked in boiling water, their starch granules soak up water, causing them to swell and soften. This increases their fluid content as much as sixfold, transforming them from one of the driest foods to one of the wettest.
Cooking can make certain foods lose small amounts of fluid. Cooking meat, for example, causes it to lose 20 to 30 percent of its original water content. But because foods like meat, poultry, and fish are inherently rich in water, they still contribute to our overall water needs.
Soup, fruits, and vegetables are all more than 80 percent water, so adding more of these foods to your diet can contribute to your overall hydration. You can also count any beverage, including milk, juice, soda, and even coffee and tea (their diuretic role has been exaggerated).