Dehydration is a major problem for humans, and it’s especially intriguing when people exercise, run marathons, or are older and fail to drink enough fluids. But there’s also, as in anything else, the tendency to overhydrate, and we hear very little about that.

I worked in several psychiatric hospitals where patients were constantly monitored for hydration, but occasionally, we would have a patient who would drink excessive amounts of water, and it would turn tragic. Some patients also failed to drink enough water while exercising vigorously in an overheated gym at 95°F. That particular patient died on the basketball floor.

One important point to note: certain psychiatric medications can dull a person’s ability to sense being overheated or even being cold. This works both ways, and either extreme can be fatal. I’ve also known of one patient who went out in a storm without a jacket and disappeared into the woods. They found him hours later, a victim of hypothermia.

This isn’t usually my area of focus, but I believe it’s so important, especially with the temperatures that are being seen with climate change, that everyone, regardless of whether we’re amateur athletes, obsessive house cleaners, or elderly, should be aware of how much fluid we take in each day. Staying hydrated is one of the most important wellness tips, and I hesitate to call it a “tip” because it’s more than that.

We’ve been told our whole lives to drink more water. Eight glasses a day (a medical myth). Maybe more. Carry a water bottle everywhere. Hydrate, hydrate, hydrate. And honestly, for most people, staying hydrated is genuinely good advice. But here’s the thing nobody’s talking about — you can actually drink too much water, and in some cases, it can kill you. It’s called polydipsia, and it’s more complicated and more dangerous than most people realize.

To be clear, this isn’t about sipping a little extra when you’re thirsty on a hot afternoon. We’re talking about drinking water compulsively — sometimes in frightening amounts — to the point where your body simply can’t handle it anymore. And when that happens, the consequences can go from uncomfortable to life-threatening faster than most people would ever expect.

So, What Exactly Is Polydipsia?

Polydipsia is the medical word for compulsive, excessive drinking of fluids — and it comes in a couple of different forms. One type, called psychogenic polydipsia, is driven by mental health conditions. It shows up most often in people living with schizophrenia, but it can also appear in those dealing with bipolar disorder, depression with psychotic features, anxiety disorders, and even anorexia nervosa, where some people use water to try to suppress hunger.

The other type, called dipsogenic polydipsia, shows up in people who’ve genuinely convinced themselves that drinking massive quantities of water is simply a healthy lifestyle choice. Wellness culture and social media promote the idea that drinking more water always leads to better health, contributing to the rise of this version of polydipsia.

Both forms can lead to the same terrifying outcome: a condition called hyponatremia, which is basically a dangerous drop in your blood sodium levels. And low sodium doesn’t just make you feel a little off. It can cause your brain to swell. It can cause seizures. It can put you in a coma. It can kill you.

The science behind it is actually pretty straightforward, even if it sounds a little wild. Sodium is the mineral that helps keep the right balance of fluids inside and outside your body’s cells. When you flood your system with more water than your kidneys can clear — and healthy kidneys can process only about 1 liter per hour — that extra water dilutes your sodium.

Once that happens, water begins seeping into your cells to try to balance things out. Most cells can handle a little swelling. But your brain is packed tightly inside a rigid, bony skull with almost no room to expand. When brain cells start swelling, pressure builds fast. And that’s when things go from uncomfortable to life-threatening in a hurry.

Our nervous system needs to keep sodium and potassium in balance. That’s done by the sodium-potassium pump, which helps everything work properly. If the sodium level gets out of sync with what the body needs, we’re in trouble.

Who’s Most at Risk — and What to Watch For

It’s easy to assume this only happens to people with serious mental health struggles or extreme athletes pushing their limits. But the truth is that the range of people who can be affected is broader than most of us think. Those who tend to be most vulnerable include:

• People with psychiatric conditions like schizophrenia or bipolar disorder, who may drink compulsively without fully recognizing the danger

• Endurance athletes — marathon runners, triathletes, and military trainees — who consume large volumes of water during intense physical exertion without properly replacing their electrolytes

• People using MDMA (ecstasy/molly) at concerts or festivals, since the drug raises body temperature, creates intense thirst, and simultaneously interferes with the body’s ability to flush out fluids

• People taking certain antidepressants or antipsychotic medications can experience extreme thirst as a side effect

• Anyone caught up in an extreme wellness trend or detox plan that involves drinking unusually large amounts of water every single day

The signs that something’s going seriously wrong can look deceptively mild at first, which is part of what makes polydipsia-related illness so dangerous. Here’s what to watch for:

• A persistent headache that just won’t quit

• Nausea or vomiting

• Muscle cramping, weakness, or twitching

• Confusion or disorientation — feeling foggy or unlike yourself

• Unusual fatigue or drowsiness that comes on suddenly

• Swelling in the hands, feet, or face

• In severe cases: seizures, loss of consciousness, or coma

The trickiest part of all this is that some of these symptoms can look a lot like dehydration, which can actually lead people to drink even more water and make the situation significantly worse. If you or someone nearby has these symptoms and you can’t tell if it’s too little or too much water, don’t try to figure it out. Get medical help immediately.

What to Avoid — and How to Keep Yourself Safe

There’s a lot of well-meaning but genuinely problematic advice floating around when it comes to hydration. Here’s what you’ll want to avoid:

• Don’t treat the ‘eight glasses a day’ rule as a hard requirement — research has found there’s actually no solid scientific support for it, and for some people it can cause real harm

• Don’t push yourself to drink water when you’re not thirsty just because you think it’s ‘the healthy thing to do’

• Don’t drink more than about a liter of water per hour, even during exercise

• Don’t rely on water alone to stay hydrated during long or intense physical activity — electrolytes, especially sodium, matter just as much as the fluid itself

• Don’t dismiss warning signs because ‘it’s just ‘water’ — that assumption is exactly what makes polydipsia so dangerous

The best rule of thumb for healthy adults? Let your thirst be your guide. The body is remarkably adept at telling you when it needs water — and when it doesn’t. If your urine is pale yellow, you’re almost certainly doing fine. If it’s completely clear and you’re still drinking, that’s a signal to slow down and give your kidneys a chance to catch up.

If you or someone you love seems to be drinking compulsively — especially if it seems connected to a mental health condition — it’s worth talking to a physician. Polydipsia tied to psychiatric illness is notoriously difficult to manage without professional support, and simply trying to cut back on water intake without guidance can be both frustrating and risky. There are treatment options available — including behavioral therapy and, in some cases, medication adjustments — that can make a genuine difference.

Water is life. That’s not just a saying — it’s basic biology. But like so many things that are genuinely good for us, too much of it can turn against you. Understanding the real risks of overhydration isn’t about making yourself afraid of your water bottle. It’s about drinking smart, listening to your body, and knowing when something feels off. Because staying healthy isn’t just about what you put into your body — it’s also about how much.