Got brain fog? You know that feeling of mental fatigue that clouds your thoughts, keeps you from concentrating, and just generally makes you feel crummy? While it’s not technically a medical diagnosis, it’s pretty common—and it can happen for a number of reasons. If you’ve been feeling ‘blah’ for some time, you may seek out an expert who can help you navigate those symptoms.

Enter neuroscientist and author of Biohack Your Brain Kristen Willeumier, Ph.D.: She sees plenty of patients looking to cut through the mental noise and feel sharp once again: “If I’m going to work with somebody and help them to have a better memory, the first thing I say is: ‘How much [water] are you drinking?”

Why Hydration Is Huge For Brain Health

Your brain is literally made up of water (75% to be exact!), so it needs fluids in order to work properly. “[Water is] going to help keep your blood pressure normalised; it’s going to help flush out [waste] from your cells; and it keeps your cells metabolically active and healthy,” Willeumier adds, all of which are important functions for brain health.

Not to mention, water is crucial for memory and mental clarity.

Willeumier explains that even if you have a 1 to 2% drop in hydration, you can start to have symptoms associated with brain fog, like fatigue, headache, and poor concentration. Another study shows that when a group of young, healthy women restricted their water intake to no more than 6 ounces in one day, they performed worse on cognitive tests that required visual and working memory.

After they drank enough water and repeated the tests, their executive function went back to baseline.

The bottom line?

Dehydration (even a mild drop) can sabotage your mental game and make you feel a bit under the weather. That’s why, Willeumier notes, “One of the first things I do when I teach people about taking care of their brain health is to make sure they are drinking their daily requirement [of water].”

How To Make Sure You Drink Enough Water

So exactly how much water should you be drinking?

The answer is that it differs for everyone depending on your environment, activity level, and diet (example: Keto folks or those who simply eat more meat may need to drink more water to match the dehydrating diet), but experts generally recommend you drink half your bodyweight in ounces of water.

So fill up your water bottle and get sipping! If you need more help reaching your personal hydration benchmark, Willeumier says you can opt for hydrating foods as well to meet the threshold. “You can get 20% of that water from hydrating fruit, vegetables, or green juices,” she says.

Try adding hydrating superstars to your glasses of water, like cucumbers, chia seeds, or a pinch of sea salt. Or you can opt for a fibre-rich green smoothie that holds on to hydration in your body like a sponge. Get creative—just get your fluids.

If you’re experiencing brain fog symptoms and aren’t sure where to turn, Willeumier’s first tip is to check your hydration levels. It’s a simple experiment: Try upping your water intake and see if the crummy feeling subsides.