How Much Water Should You Drink Each Day During A Heat Wave

You may have heard different rules of thumb about how much water you should be drinking on an average day, such as eight 8-ounce glasses. But in the midst of a heat wave, do such rules of thumb still hold or instead become all thumbs?

Well, your hydration requirements may be different when you are roasting under the hot sun like a rotisserie chicken, sweating like a water sprinkler or spending your days in dry, dry air conditioned areas. Plus, people are—surprise, surprise—very diverse. A simple one-size-fits-all number will not apply to every person and every situation. Rather than following a specific amount of water to drink each day, it’s important to monitor and follow a particular body function. And, spoiler alert, this body function can help determine whether “urine” in good or bad shape when it comes to hydration.

First, let’s look at the four most common hydration simple rules of thumb:

• The six to eight 8-ounce glasses of water a day rule. This one is easiest to remember, especially if you think eight by eight. So that aspect is helpful. But as indicated earlier, a simple one-size-fits all rule doesn’t account for differences in people and circumstances.
• The about 15.5 cups (3.7 liters) of fluids a day for men and 11.5 cups (2.7 liters) a day for women rule. OK, this rule divides people into men and women because, you know, men are from Mars and women are from Venus, right? Well, not really. Not all women and not all men are the same. Even though on average, men may have larger body sizes than women, there is tremendous diversity within each sex. For example, will a 5-foot-3 male jockey always need more fluid than a 6-foot-3 female WNBA player?
• The multiply your body weight in pounds by 0.5 to get the number of ounces of water you should drink rule. So, for example, a 150-pound person should be drinking at least 75 ounces of water per day. This accounts for body weight. But shouldn’t a person’s physical activity matter? Otherwise, why bother putting the cups of water along the route of a marathon race?
• The add 12 ounces of water each day for every 30 minutes of exercise rule. This one is from the American College of Sports Medicine and does account for physical activity to some degree. But all physical activity is not the same. Chasing around squirrels in the backyard during a snowstorm isn’t the same as playing golf in spring or cheese rolling in the middle of a summer heat wave.

All of these can give you a general ballpark number, especially if you are debating between drinking one thimble versus 20 gallons of water a day. But rather than stick strictly to any of the above numbers, the key is to pay close attention to your body and what it is telling you.

Now, it may seem like thirst holds the biggest megaphone in your body in this situation. Certainly, when you are thirsty, it is a good idea to drink water, as long as you make sure you get enough electrolytes, too, so that you don’t suffer something like hyponatremia. However, thirst can often be unreliable. The absence of thirst doesn’t necessarily mean that you body doesn’t need more hydration. Relying solely on thirst to tell you to drink more water can be like relying solely on your fellow party-goers to keep you from drinking too much alcohol.

Also, don’t wait until you experience signs of dehydration such as headaches, lightheadedness, dizziness and changes in the turgor of your skin. Dehydration can lead to serious complications, such as heat cramps, exhaustion and stroke, urinary tract infections, kidney stones, kidney failure, seizures, drops in blood pressure and shock. So, waiting too long can be a highway to the danger zone, to quote that Kenny Loggins song.

No, the number one thing to pay attention to is, well, number one—your urine and how often you pee. If your kidneys are functioning correctly, they will hold onto water when you are dehydrated and let more water go into urine when you are well-hydrated. This is reflected in the color of your urine. The lighter your urine is, the more water your urine has compared to the waste products that your kidneys are excreting.

Conversely, the darker your urine is, the more your kidneys are keeping water from flowing into your urine. Ideally, your urine should remain a very pale yellow or even clearer. Darker colors mean it’s time to go drinking—drinking water, that is.

You also should be peeing once every two to four hours or so. If you have to get out a calendar to determine when you last went number one, you are taking in far too little fluids. Of course, the amount of urine matters, and urinating just a trickle doesn’t count. In other words, mind your pees and Qs, with Q standing for quantity.

If you continue to pay attention to your urine each day, you should soon get a sense of how much water you should be drinking on a daily basis. This will likely go up when you exert yourself more, when the air is dry or when it is hotter outside. Once you’ve got a sense of what your regular intake should be, you can always add more when circumstances call for it.

And be proactive and preemptive about these circumstances. For example, each time you are about to go outside into hot weather, drink a tall glass of water. The same applies for when you are about to go exercise. If you find yourself going to the bathroom every half hour, you can always titrate your fluid intake downwards.

This is yet another situation where you should be listening to your body, which can be difficult when you have all sorts of distractions around you. So when you do go number one, paying attention to your urine should be your number one focus.