Everyone needs water, but drinking water is a habit, not a reflex. “Thirst is a really poor indicator of hydration,” said Melissa Mahoney, an athletic trainer at the Marine Corps Recruit Depot in San Diego. “People need to shift their mindset when thinking about water not so much as a reflex or an urge, but it really is a behavior.” By the time your body actually wants to drink water, it’s already dehydrated, she said.

Dehydration results from not replacing fluids and electrolytes that are either lost from illness, physical exertion, or even from sitting, said Dr. Chad Hulsopple, an assistant professor of family medicine at Uniformed Services University of the Health Sciences. “Even at rest, our body loses fluids slowly due to evaporation from the skin and moisture in the breath. It is essential to consume fluids and electrolytes to stay hydrated even when not exercising.”

According to Hulsopple, people may experience different symptoms of dehydration aside from thirst, such as dry mouth, dry lips, headache, or dizziness. Dehydration is preventable and could lead to heat-related illnesses. Physical exertion and humidity can contribute to dehydration and heat-related injuries, such as heat exhaustion and heat stroke. Reports of both increased among active service members between 2014 and 2018, according to a recent Medical Surveillance Monthly Report.

Multiple factors could play a role in heat-related illness, including obesity, personal protective equipment—such as helmets or thick and long-sleeved clothing, and gastrointestinal illnesses and those involving a fever, explained Hulsopple. Mahoney found most of the heat-related injuries among the recruits at the Marine Depot in San Diego were due to upper respiratory infection or pneumonia. Someone sick with a fever who goes out to exercise increases the risk of heat-related injuries, she said.

So how much water should you be drinking? On average, a person engaged in physical activity that lasts less than one hour should be drinking 16 ounces to 32 ounces of water every hour, said Mahoney. “The easy guideline to remember is to drink half your body weight in fluid ounces,” she said, adding not to exceed more than 48 ounces of water per hour. “Your kidneys specifically can’t process the water that quickly and if you consistently drink that much, you run the risk of hyponatremia or an overhydrated state.” Hyponatremia is serious and potentially fatal, added Hulsopple.

Mahoney teaches that the behavior of consuming water requires being mindful. “Find what works best for you. For me, personally I’ve found I drink more water when I am drinking out of my metal water bottle with a straw,” she said, noting others may like keeping track of water intake by hour. It’s difficult to give a blanket statement on how to know if you’re adequately hydrated because there are so many factors that contribute to each individual case and rate of fluid loss, cautioned Hulsopple. One simple tool to measure hydration involves urine output and color. Dark colored urine is an indication of dehydration. A well-hydrated person will urinate five to eight times a day. “Regular urination that is pale or clear colored is a visual sign of adequate hydration,” he said.

Whether room temperature water, sparkling water or ice water, the message is simple, just drink water. If adding flavoring to water helps increase water intake, Mahoney added, “Don’t beat yourself up about that, you’re getting more fluids than you were before so those things are good.” Water as a nutrient can also be found in food and other beverages, such as coffee and sugary drinks. She cautioned, however, some substances can affect hydration, including alcohol and performance supplements like creatine.

“Supplements and other prescribed medications can increase susceptibility to heat illnesses and dehydration,” added Hulsopple, who referenced the DoD’s Operational Supplement Safety guidelines for additional information. The Warrior Heat and Exertion Related Event Collaborative also provides educational resources, policies, and procedures for the prevention and management of heat illness and other related medical conditions. Always discuss any questions about how current medications, work environment, or supplements affect hydration with a doctor.

When it comes to drinking coffee, soda, or teas, “moderation is key to everything,” said Mahoney. “You don’t need to eliminate teas or coffee or sodas in terms of hydration, but your main substance should be water.”

Water is important for various bodily functions, including removing waste, regulating body temperature, and affecting blood volume and brain function. In stressful times, water has another benefit as well. “Sipping water encourages you to regulate your breathing,” said Mahoney. “So if you’re stressed out, drinking water is going to help your body and also help your mind.”