Drinking water is essential to survive. Especially for those who are highly active throughout the day. But, drinking too much water without electrolyte replenishment can significantly lower sodium levels. This is better known as a condition known as hyponatremia. 

Your body is a machine that needs to be able to maintain a balance of fluids & electrolytes. This is especially true for sodium, which is ideal for nerve, muscle, & cellular function. Sodium is the primary electrolyte in extracellular fluid and helps regulate: Fluid distribution, nerve impulses, muscle contractions, & blood pressure.

So what happens when you drink large volumes of water without sodium replenishment? You essentially dilute the sodium in your bloodstream. This creates a low concentration of sodium relative to water — a hypo-osmolar state — causing water to enter cells and swell them (including brain cells). Even mild-to-moderate sodium dilution often manifests with fatigue, weakness, reduced cognition, and low energy.

Drinking large volumes of water without electrolyte replenishment is especially risky for these populations below:

Population

Why It Matters

Athletes

Sweat contains sodium. Replacing fluid with plain water leads to sodium loss + dilution. Marathon runners and triathletes are high risk.

Fasting/detoxing individuals

Low dietary sodium + high water intake = recipe for hyponatremia.

People with kidney/liver/heart issues

Fluid regulation may already be compromised.

Elderly or certain psychiatric patients

May drink excessively (polydipsia), risking dilution.

When should I integrate replenishment?

When drinking lots of fluids, especially during:

• Exercise
• Illness (fever, vomiting, diarrhea)
• Hot weather
• Fasting

Make sure to replenish:

• Sodium
• Potassium
• Magnesium
• Chloride

Solutions:

• Electrolyte powders
• Sports drinks (with caution re: sugar)
• Salted foods (e.g. broth, pickles, olives)
• Homemade oral rehydration solution (ORS)

Peer review supporting articles:

A comprehensive systematic review of adult cases of hyponatremia from excess water intake reported mean serum sodium of 118 mmol/L, with many patients experiencing fatigue, confusion, and lethargy, and serious complications in ~13% of cases https://pmc.ncbi.nlm.nih.gov/articles/PMC8663108/?utm

A clinical biomedical review states:

“Even mild hyponatremia is associated with increased hospital stay and mortality,”

and symptoms extend from weakness and nausea to lethargy and attention deficits https://pubmed.ncbi.nlm.nih.gov/35852524/

Multiple sources, including health and medical reviews, consistently list fatigue, lethargy, and weakness as hallmark symptoms of hyponatremia caused by sodium dilution https://www.verywellhealth.com/hyponatremia-low-sodium-2488674?utm_

A 75-year-old woman with marked hyponatremia presented with progressive fatigue and somnolence, resolved after correcting sodium levels https://pubmed.ncbi.nlm.nih.gov/11341300/

A chronic case in a 66-year-old patient on diuretics experienced years of fatigue, confusion, and headaches, ultimately linked to persistent mild-to-moderate hyponatremia https://pubmed.ncbi.nlm.nih.gov/34464373/

A patient with overriding endocrine hyponatremia (Sheehan’s syndrome) had marked fatigue, nausea, and cognitive slowing, improving after hormone and sodium correction https://jmedicalcasereports.biomedcentral.com/articles/10.1186/1752-1947-7-227?utm

In an ICU patient cohort, most with euvolemic hyponatremia reported lethargy and malaise, and some progressed to confusion and seizures. The rapidity of onset correlated strongly with symptom severity https://pmc.ncbi.nlm.nih.gov/articles/PMC5752789/?utm

Finding

Details



Dilutional hyponatremia from water alone

Documented when intake exceeds excretion capacity (e.g. >0.8–1 L/hr), lowering sodium to ~118 mmol/L or less (PMC).

Fatigue & low energy common symptoms

Especially in mild/moderate hyponatremia—fatigue, lethargy, muscle weakness, attention deficits, cognitive slowing (PubMed, Wikipedia, Health, Verywell Health).

Case evidence

Real‑world cases (adults, elderly) showing profound fatigue tied to sodium‑diluting conditions (PubMed, BioMed Central, PubMed).

Clinical reviews

Emphasize even mild hyponatremia can impact energy, attention, physical wellbeing (PubMed, PubMed, Verywell Health).