Hydration and Electrolytes: Why Drinking More Water Isn't the Answer

A recent case

A patient I will call Margaret came into an emergency room recently for shortness of breath, nausea, and a few days of feeling unlike herself. She is in her seventies. She has a history of cardiac disease and a pacemaker, a few stents, and a hiatal hernia and gastroparesis that occasionally flare. She is on Jardiance (an SGLT2 inhibitor for diabetes), Ramipril (an ACE inhibitor for blood pressure), and a handful of other reasonable medications. She drinks four to five bottles of water a day, on purpose, because she has been told to stay well hydrated. Her workup was, in clinical terms, mostly unremarkable. Her heart looked fine on echo. Her cardiologist did not see anything acute. Her kidneys were not damaged. The only lab that was clearly off was her BUN at 29.7 - a sign of dehydration, not kidney damage. Her heart rate was being paced more than usual by her pacemaker, which is what the heart does when it senses the body needs more output. She was, almost certainly, under-hydrated and electrolyte-depleted, despite drinking what most clinicians would consider plenty of water. That is the whole point.

Why drinking plain water alone does not hydrate you

Hydration is not the same thing as water intake. Hydration is whether water is inside the right compartments of your body - in your blood plasma, in your tissue, and inside your cells where it can actually do work. Plain water has no electrolytes. When you drink a bottle of it, the water enters your bloodstream and the kidneys read the falling osmolality (the concentration of solutes in blood) as a signal to dump that water through urine. Within an hour or two, most of it has come back out. You stay dehydrated despite drinking. The way water actually stays in your system is by being held there by sodium, potassium, and to a lesser degree magnesium, calcium, and chloride. These minerals create the osmotic gradient that keeps water in tissue and inside cells where you need it. Without enough of them, water flows through you instead of into you. This is not a fringe view. It is the same physiology that explains why hospital IV bags always contain salt. There is no such thing as a "bag of water" given through an IV. A 0.9% normal saline bag has 154 mEq/L of sodium and 154 mEq/L of chloride in it. Even D5W (5% dextrose in water), which sounds salt-free, is paired with electrolytes for any sustained infusion. We never give plain water through an IV because plain water alone would shift fluid in dangerous ways. The same biology applies, less dramatically, to what you sip from a glass.

Why salt and blood pressure are not opposites

This is the part where most public health messaging goes off the rails. Patients hear "you have high blood pressure, watch the salt" and translate that into "salt is the enemy." For some people in some contexts that is true. For most people most of the time it is not. Two things help:

1. High blood pressure is mostly a problem when salt comes in without water. A bag of chips eaten while dehydrated will pull water from tissue into the blood vessels to dilute the sodium load, and the resulting volume spike is what raises pressure. A pinch of salt added to a glass of water - so the sodium comes in with the fluid it needs - is a fundamentally different physiologic event.
2. Dehydration artificially lowers your blood pressure reading. When you are running low on intravascular volume, the cuff reads a number that is below your real, well-hydrated baseline. So when you rebuild hydration with water plus salt, the blood pressure number sometimes comes up - not because you "caused" hypertension, but because the cuff is now reading what your body actually runs at when it has the volume it needs. That is a healthy correction. The right response is to manage blood pressure properly with medication if needed, not to strip salt out of a hydration protocol.

There is a separate, real conversation about salt restriction in specific populations: people with severe heart failure, certain kidney conditions, very high baseline blood pressures (180/110 and above), and a few others. That conversation belongs with your physician. Most adults are not in those categories.

What to actually do

The minimum-viable version:

1. Add a pinch of low-sodium salt to your water through the day. Low-sodium salt is sold over the counter in any grocery store. The "low-sodium" label is a little misleading - it contains both sodium chloride and potassium chloride, which is exactly the balance most people are short on. A pinch in each glass is enough. You are not trying to taste salt; you are trying to give the water something to anchor to.
2. Aim for water that has electrolytes more often than water that does not. You do not have to do this with every sip - having a plain glass of water is fine. But the default through your day should be water + a pinch of salt, especially if you sweat, are out in the heat, are on the medications below, or are recovering from any kind of GI bug.
3. Get your magnesium from a separate source. Salt does not cover magnesium. We use glycinate, malate, or L-threonate depending on the goal (sleep, GI tolerance, cognitive). We avoid magnesium oxide (poor absorption) and magnesium citrate unless we are specifically trying to move the bowels. Read our magnesium glycinate clinical guide for the dosing and form discussion - we will not duplicate it here.
4. Watch for the early signal. Fatigue, fogginess, lightheadedness when you stand, mild nausea, headaches, salt cravings (potato chips and pretzels are the body asking), muscle cramps overnight, constipation. All of these can be the first signs of under-hydration long before a lab tells you.

The packet option (LMNT, optional)

If carrying low-sodium salt around is not practical, packet-based electrolyte mixes are a reasonable convenience. LMNT is the one we mention most often because the formulation is clean - sodium, potassium, magnesium, no sugar, no fillers - and the sodium dose per stick (1000 mg) is the most useful for athletes or anyone working in heat. Disclosure: that link is a referral link that may earn the practice a small credit. It does not change what we recommend and most patients do this with a grocery store salt jar at a tenth the cost. See our supplement guide framework for how we think about product picks. Try LMNT - the referral link, if you want the convenience option.

Who needs to pay extra attention

The basic protocol is enough for most adults. These are the categories of patient where under-hydration shows up earlier and harder, and where the protocol should be more deliberate.

SGLT2 inhibitors (Jardiance, Farxiga, Invokana)

These diabetes medications work by pushing glucose out through the urine. The trade-off is that water follows the sugar. Patients on SGLT2 inhibitors are functionally on a mild, continuous diuretic. Plain water alone is even less effective for them than for the general population. Electrolyte attention is not optional - it is part of the care plan.

Diuretics (loop, thiazide, potassium-sparing)

Different diuretics shift electrolytes differently. Loop and thiazide diuretics tend to deplete potassium and magnesium. Potassium-sparing diuretics (and ACE inhibitors like ramipril or lisinopril) tend to retain potassium. The point is that the medication is moving the electrolyte picture, and a deliberate hydration plan is part of the medication being safe.

Acute GI illness (vomiting, diarrhea, gastroparesis flare)

This is where most of the avoidable ER visits for dehydration come from. A 24-hour stomach bug can deplete a remarkable amount of electrolytes. The recovery protocol is more aggressive than the maintenance protocol. Plain Pedialyte (or a frozen Pedialyte pop) is reasonable here for short stints. Sports drinks are not - the sugar load makes the GI worse.

Older adults

Two physiologic shifts compound: the thirst response is blunted with age (you do not feel thirsty until you are already meaningfully dehydrated), and the kidneys are less efficient at conserving water. Add any of the medications above and the picture compounds further. Older adults should not wait until they feel thirsty.

Summer heat and active days

Sweat takes both water and salt out simultaneously. A serious sweat session - long bike ride, hot yoga, gardening for three hours in July, a Phillies game in the upper deck on a 95-degree day - meaningfully changes the math. This is where the LMNT-style packet or a deliberately stronger pinch of salt is worth the trouble.

Athletes

Endurance and high-intensity athletes are in a different metabolic context. The general guidance still applies, but volume goes up substantially. A daily sodium intake well above standard recommendations is normal for athletes training in heat. Talk to your physician or a sports-medicine specialist about your particular numbers.

Pregnancy

Hydration and electrolyte needs are higher in pregnancy. Sodium needs go up, not down (despite older guidance to the contrary). Pregnant patients should work this out with their obstetrician.

The Gatorade question

Sports drinks are a reasonable rehydration option in a narrow context: an elite athlete burning through significant glycogen during a sustained athletic effort needs both the carbohydrate and the electrolytes simultaneously. That is a specific physiologic situation and most people sipping a Gatorade at a Wawa do not match it. For everyone else, sports drinks deliver about 30 grams of sugar per 20 ounce bottle alongside the electrolytes you actually want. The sugar load:

• Drives insulin and crashes you within an hour or two
• Defeats the purpose if you are using the drink to hydrate during illness
• Compounds metabolic risk over time when used daily
• Frequently outperforms the electrolyte signal it was bought to deliver

We do not recommend Gatorade, Powerade, Vitaminwater, or most colored sports drinks as part of a routine hydration plan. Low-sodium salt in plain water is cleaner, cheaper, and works better. See our digital health literacy guide on supplements and marketing for the broader framing on how wellness products like these are sold versus what they actually deliver. Pedialyte is a different category - it was designed for pediatric rehydration during illness, the sugar load is lower, and it is reasonable for short stints during GI bugs. A frozen Pedialyte pop on a hot day is a fine occasional treat. It is not a daily product for healthy adults.

When under-hydration shows up in the ER

Most people do not know about this part, and it is why Margaret's case matters. Under-hydration shows up at the emergency room dressed as more serious problems:

• Demand ischemia. When your heart is working harder than usual because the body is volume-depleted, the increased oxygen demand on the heart muscle can cause chest pain that looks like an acute coronary event. The cardiac enzymes go up. The ECG can change. The workup costs thousands of dollars and ends with a "we did not find an acute heart attack" discharge, when the actual problem was dehydration.
• Acute kidney injury. A modest BUN rise is the early signal. Sustained dehydration over days raises creatinine and the eGFR (estimated glomerular filtration rate) drops. With a baseline of chronic kidney disease, this can convert a stable picture into a hospital admission.
• Falls and altered mental status in older adults. Orthostatic hypotension (the blood pressure drop when you stand up) is more pronounced when volume-depleted. A fall that breaks a hip in someone over 75 is a meaningful inflection point in life expectancy. The dehydration that caused the fall is usually invisible until the fall happens.
• Pacemaker pacing more often than usual. A pacemaker is set to support the heart when the heart's own pacing falls below a threshold. When the body is volume-depleted, the heart often needs to work harder, and the pacemaker steps in more frequently. Patients sometimes notice this as feeling their pacemaker "kicking in" more.

Most of these scenarios resolve quickly once volume and electrolytes are restored. None of them should have to reach the emergency room.

Key Takeaways

• Plain water alone does not hydrate you. Without sodium, potassium, and magnesium, most of what you drink leaves through urine within an hour or two.
• A pinch of low-sodium salt in your water through the day is the cheapest, simplest, most underused tool in primary care. Grocery store, over the counter, a few dollars a year.
• Salt and blood pressure are not opposites. Dehydration artificially lowers BP readings. Rebuilding hydration sometimes makes the number come up to its real value. That is a healthy correction, managed with BP medication if needed - not by stripping out the salt.
• Magnesium is its own conversation. Glycinate, malate, or L-threonate. Not oxide, not citrate. See our magnesium glycinate guide.
• Sports drinks are sugar and marketing in a bottle for most people. Grocery-store low-sodium salt is cleaner, cheaper, and works better.
• The categories that need to pay extra attention: SGLT2 inhibitors (Jardiance), diuretics, GI illness, summer heat, older adults, endurance athletes, pregnancy.
• Under-hydration shows up in the ER dressed as more serious problems: demand ischemia, acute kidney injury, falls in older adults, pacemaker over-pacing. Most of these never had to reach the emergency room.

Scientific References

1. Sterns RH. Disorders of plasma sodium - causes, consequences, and correction. New England Journal of Medicine. 2015;372(1):55-65.
2. Cogswell ME, Loria CM, Terry AL, et al. Estimated 24-hour urinary sodium and potassium excretion in US adults. JAMA. 2018;319(12):1209-1220.
3. Mente A, O'Donnell M, Rangarajan S, et al. (PURE Study Investigators). Urinary sodium excretion, blood pressure, cardiovascular disease, and mortality: a community-level prospective epidemiological cohort study. Lancet. 2018;392(10146):496-506.
4. DiNicolantonio JJ, O'Keefe JH. The history of the salt wars. American Journal of Medicine. 2017;130(9):1011-1014.
5. Stookey JD, Constant F, Popkin BM, et al. Drinking water is associated with weight loss in overweight dieting women independent of diet and activity. Obesity. 2008;16(11):2481-2488.
6. Ferreira JP, Zannad F, Pocock SJ, et al. Interplay of mineralocorticoid receptor antagonists and empagliflozin in heart failure: EMPEROR-Reduced. Journal of the American College of Cardiology. 2021;77(11):1397-1407. (SGLT2 / volume context.)
7. Sica DA. Sodium and water retention in heart failure and diuretic therapy: basic mechanisms. Cleveland Clinic Journal of Medicine. 2006;73(Suppl 2):S2-S7.
8. Stookey JD. Higher predicted vasopressin secretion is associated with greater chronic kidney disease prevalence in a large general adult population. American Journal of Nephrology. 2011;34(5):417-426.
9. Armstrong LE, Casa DJ, Maresh CM, Ganio MS. Caffeine, fluid-electrolyte balance, temperature regulation, and exercise-heat tolerance. Exercise and Sport Sciences Reviews. 2007;35(3):135-140.
10. Murray B. Hydration and physical performance. Journal of the American College of Nutrition. 2007;26(5 Suppl):542S-548S.

Related at Fishtown Medicine

• Magnesium Glycinate Clinical Guide - forms, dosing, who needs which version
• How We Choose Supplements - the three-gate framework
• IV Vitamin Therapy: Expensive Urine or Real Tool? - when drip bars are real medicine and when they are theater
• Digital Health Literacy - the broader frame for sports drinks, wellness marketing, and electrolyte hype
• UV Index in Philadelphia: What to Do at Every Tier - hot-weather context
• Severe Weather in Philadelphia: What to Do - hydration and heat / cold edge cases
• Stroke Prevention in Philadelphia - the cardiovascular context behind much of this

Medical Disclaimer: This article is for educational purposes only and is not medical advice for any individual. Hydration and electrolyte needs depend on your specific medical history, medications, kidney and heart function, activity level, and physiology. The patient case described uses a pseudonym and rounded details, with identifying information changed or removed. If you have heart failure, kidney disease, advanced hypertension, or are taking diuretics or other medications that affect electrolytes, work out your specific protocol with your physician before making changes.