If you're trying to gain weight, drinking more water isn't the answer. Adults need an average of 8 to 12 cups of water per day, regardless of whether they're trying to maintain their weight or change it. Should you get a lot of exercise or if the weather is particularly hot, you may need even more water than usual to stay properly hydrated. Drinking more water than you need won't help you gain weight, however, because water has no calories.
Calories for Weight Gain
Because water is a calorie-free beverage, it doesn't cause actual gains in body fat -- although retaining extra fluid can tip the scale a little higher. To put on a pound of body tissue comprised of fat and muscle, you need to consume an extra 3,500 calories. People trying to gain weight are often advised to eat 500 extra calories per day to help them gain at a healthy rate of about 1 pound per week.
Water Weight Considerations
While drinking water doesn't cause true weight gain of muscle tissue or fat, each cup of water weighs about half a pound, so right after you drink a glass of water your weight may temporarily increase by this amount until it works its way through your system and is excreted through your urine. If your water intake is spread throughout the day, it isn't likely to cause much fluctuation in your weight, but drinking multiple cups of water in quick succession could cause your weight to temporarily increase by a couple pounds.
Water weight, also called bloating, may result from too much dietary sodium. You may notice it after eating sodium-laden foods such as pickles, deli meats and processed foods like frozen pizza or flavored rice mixes. The extra sodium causes your body to hold onto more water than usual, temporarily increasing your weight. Drinking more water is actually one way to help the body to flush out any extra fluid. Eating more potassium-rich foods such as bananas, beans and avocado can help, too, because potassium helps your body maintain the proper water balance.
Water and Weight Changes
Drinking extra water is actually more likely to cause you to lose weight than to gain weight. A study published in Obesity in 2012 found that as people drink more water during a weight-loss diet their weight loss increases. Another study, published in Obesity in 2011, found similar results, noting that drinking 2 cups of water before each meal increased weight loss, possibly because it led to people eating less during the meal.
Since water right before meals may fill you up and cut your appetite, try drinking it between meals instead. Beverages with calories count toward your fluid intake, too, so the 8 to 12 cups of fluid you need daily don't have to all come from water.
Nutritious Beverages to Drink for Weight Gain
If you want to gain weight, consider other nutritious beverages that have calories. Homemade smoothies are a good option, as you control the ingredients and can add a significant number of calories. Use Greek yogurt, milk, nut butter, cocoa powder, a banana and perhaps a dash of honey or maple syrup for a nutritious, delicious smoothie that's relatively high in calories. You can also add avocado, nuts, flaxseed oil, chia seeds or dry milk powder to add calories in the form of protein and healthy fats to your smoothies.
Milk and 100-percent fruit juices provide more essential nutrients and calories than water as well, if you want other beverage options. As with water, drink your caloric beverages separately from your meals, if that helps you avoid filling up on liquids instead of food.