In January 2020, 59-year-old Sean O'Donnell presented at St. Vincent's University Hospital in Dublin for what was supposed to be a routine, same-day procedure. The surgery was a success, and personnel advised him to remain well-hydrated during recovery, a normal post-operative instruction. However, within hours, the tip turned fatal. O'Donnell drank extensive amounts of water under no supervision, causing water intoxication, an uncommon but fatal condition. He also experienced cerebral swelling, seizures, and cardiac arrest before dying. His family subsequently settled a High Court claim against the hospital for failing to monitor his fluid levels and appreciate his condition rapidly deteriorating.Water intoxication or water poisoning or hyponatremia—results when the body absorbs more water than it can eliminate, lowering blood sodium levels. Sodium is essential in maintaining fluid balance, nerve function, and muscle contraction. When it falls below a certain level, fluids move into cells and cause them to swell. In the brain, this causes intracranial pressure to rise, resulting in changed mental status, seizures, and death if left untreated.While healthcare providers consistently stress hydration, especially following surgery, the line between adequate and excess fluid consumption can be fine. Drinking to thirst is usually safe for otherwise healthy adults, who metabolize approximately 1–2 liters of water daily. Nevertheless, drinking several liters in a short period of time—like a gallon (3–4 liters) within one or two hours overloads the filtering ability of the kidneys, triggering hyponatremia.Court filings disclosed that following his surgery, Sean O'Donnell was unattended despite express instructions to "drink lots of water." Absent direction on safe amounts or observation of his consumption, he drank huge amounts of water quickly. His sodium levels dropped precipitously, resulting in cerebral edema (brain swelling) and a series of life‑dangerous complications:Hyponatremia: Life‑threateningly low blood sodium.Cerebral Edema: Brain cells bloated with fluid shift.Seizures and Cardiac Arrest: Because of disrupted neural and muscular electrical activity.The High Court heard claims of hospital staff's failure to recognize or adequately respond to O'Donnell's worsening condition. Nobody documented his fluid balance, and warning signs were ignored. Justice Paul Coffey called it "a very shocking case," pointing to the unanticipated risk lurking inside a mundane medical recommendation.Early Warning Signs Water IntoxicationEarly recognition of water intoxication can be life-saving. The initial presentation is usually mimicking a benign state and is characterized by:Nausea and vomitingHeadache and head fullnessDrowsiness or lethargyMuscle weakness, cramps, or painWith worsening of hyponatremia, neurological findings are seen: confusion, irritability, dizziness, and decreased consciousness. Physical examination may show swelling in hands, feet, or abdomen.In the hospital environment, fluid balance diagrams and frequent neurological monitoring are necessary when patients are urged to drink aggressively. Inadequate recording of intake and output—or reaction to headache or nausea complaints—places patients at risk. O'Donnell's fatality emphasizes caution whenever medical recommendation moves away from "drink to thirst" and into "drink large amounts." Risk Factors of Water IntoxicationThe body regulates water and sodium balance by renal excretion, sweat, and respiration. In cases where intake vastly surpasses output, plasma sodium is diluted. The kidneys may be able to excrete as much as approximately a liter of free water per hour, but age, renal function, drugs, and hormonal status (e.g., increased antidiuretic hormone during the postoperative period) may impair this ability.Risk factors for water intoxication are:We recommend the following actions to prevent overhydration:Rapid drinking of quantities of waterCompromised kidney function (e.g., in older individuals or those taking specific medications)Syndrome of inappropriate antidiuretic hormone secretion (SIADH)Endurance sports where athletes over-hydrate to "get a jump" on thirstClinical recognition of these factors can direct safe hydration practices, with a focus on controlled ingestion and frequent monitoring.How To Balance Hydration and Safety While Drinking WaterTo prevent overhydration, health and caregiving professionals should:Recommend "drink to thirst" instead of ordering fixed amounts of fluid.Observe intake and output, particularly post‑operatively or in high‑risk patients.Evaluate early signs—nausea, headache, confusion—and report serum sodium if suspicion is raised.Educate families and patients on safe hydration habits and hyponatremia warning signs.Water intoxication is still uncommon, but when it happens, the effects are devastating. Sean O'Donnell's story sadly shows how a good‑natured medical suggestion can become deadly if not monitored adequately.