We've all heard the recommendation to drink eight glasses of water a day. The truth is, the amount of water that you need each day varies depending on age, gender, health, activity level and if you sweat a lot. The National Academies of Sciences, Engineering and Medicine (NASEM) recommends that you should hydrate by drinking when you're thirsty, and to let your body's thirst be your guide.
When it comes to how many calories are in water, it's important to know that plain, filtered water contains no calories. However, flavored water and carbonated water do contain calories. Typically, they have been sweetened with sugar or other caloric ingredients.
A calorie, which is also known as a kilocalorie, is the energy that it takes to raise the temperature of one kilogram of water by 1 degree Celsius. This is what is often meant when people say there are "x number of calories in water."
Getting enough water is important for your brain and body to function properly. Even slight levels of dehydration can impair your performance in activities involving attention, movement and immediate memory skills. In addition, your blood vessels are more likely to constrict if you're dehydrated.
In a study published in 2014, 50 overweight women who drank two cups of water half an hour before breakfast, lunch and dinner for eight weeks reported weight loss, lower sex hormone levels and appetite suppression. In order to understand how the women in this study lost weight, it's helpful to consider how consuming water may have impacted their overall calorie intake.