Background: Water intoxication — the clinical syndrome arising from ingestion of fluid volumes exceeding renal excretory capacity — produces dilutional hyponatremia with potentially catastrophic neurological consequences, including cerebral edema, herniation, and death. Despite decades of documented fatalities across diverse clinical contexts, public awareness remains critically inadequate. The proliferation of social media platforms since the early 2010s has introduced a novel and underappreciated exposure pathway: digital health misinformation that actively encourages excessive water consumption through competitive challenges, influencer-promoted hydration rituals, and viral wellness content.

Objectives: This narrative review synthesizes the published literature on water homeostasis, the pathophysiology of hyponatremia and cerebral edema, documented clinical cases of water intoxication across all etiological categories, and the emerging evidence base for social media– mediated risk. Epidemiological, toxicological, neurological, and public health dimensions are considered in an integrated framework.

Methods: A systematic search of PubMed, MEDLINE, Embase, and grey literature databases was conducted through August 2025. Search terms included: water intoxication, hyponatremia, exercise-associated hyponatremia, psychogenic polydipsia, cerebral edema, osmotic demyelination syndrome, social media health challenges, gallon challenge, WaterTok, and digital health misinformation. Case reports, cohort studies, clinical guidelines, systematic reviews, meta-analyses, and coroner reports were evaluated.

Results: The maximal renal excretory capacity for free water is approximately 0.8–1.0 L/hour; ingestion beyond this threshold produces dilutional hyponatremia that may precipitate cerebral edema within hours. Documented fatalities span radio contest participants (KDND-FM, 2007), military recruits, marathon runners, psychiatric patients with psychogenic polydipsia, MDMA users, and individuals attempting rapid rehydration. Exercise-associated hyponatremia affects 7–15% of marathon competitors and carries a documented case fatality rate. Social media platforms — particularly TikTok (#gallonchallenge, #WaterTok), YouTube, and Facebook — have normalized and gamified excessive water intake, creating new exposure risks that exceed historical baseline incidence. The treatment of symptomatic acute hyponatremia with hypertonic (3%) saline is established and life-saving; however, overcorrection precipitates osmotic demyelination syndrome with devastating neurological sequelae.

Conclusions: Water intoxication constitutes a preventable public health hazard whose incidence is being amplified by digital misinformation. Coordinated responses are urgently required from public health authorities, social media platforms, nutrition professionals, and clinicians. Regulatory frameworks governing health-related content on digital platforms are inadequate and require reform.