| Phenotype (category) | Onset and course/severity | Frequency / evidence quality | Suggested HPO term label |
|---|---|---|---|
| Excessive thirst / polydipsia (risk-associated behavior) | May precede intoxication for hours to weeks; drives excessive intake but is **not a universal symptom** of water intoxication. A 2023 schizoaffective-disorder case involved 16–17 glasses/day and persistent water seeking (pqac-00000056, pqac-00000057). | Not quantified for water intoxication overall; supported mainly by psychiatric case reports and subgroup literature. | Polydipsia; Excessive fluid intake |
| Polyuria after water loading (clinical sign) | Usually emerges as AVP is suppressed and excess water is excreted; may be brisk during recovery. The 2023 case produced 4.7 L in 8 hours and later 6 L in 5 hours; a naturally affected dog produced approximately 15 mL/kg/hour (pqac-00000057, pqac-00000026). | Not quantified; directly observed in human and canine cases. Polyuria may be absent or delayed when AVP remains active, renal function is impaired, or urinary retention is present. | Polyuria |
| Nausea and vomiting (symptom) | Early, nonspecific manifestations of acute hypotonicity; may progress with falling sodium. Vomiting preceded collapse and coma in the canine case and is reported in psychiatric water intoxication (pqac-00000026, pqac-00000053). | Frequency not quantified specifically for water intoxication; case-based clinical evidence. | Nausea; Vomiting |
| Headache (symptom) | Typically acute and potentially progressive; reflects developing cerebral edema or increased intracranial pressure. | Frequency not quantified specifically for water intoxication; established in clinical reviews rather than dedicated cohorts (pqac-00000008). | Headache |
| Confusion / hyponatremic encephalopathy (neurologic symptom/sign) | Acute or fluctuating; ranges from disorientation and delirium to profound encephalopathy. A 2023 patient presented aphasic and unresponsive with Na 115 mmol/L and serum osmolality 246 mOsm/kg (pqac-00000056, pqac-00000057). | Frequency not quantified; directly documented in human case reports. | Confusion; Encephalopathy; Delirium |
| Ataxia (neurologic sign) | Usually acute and may accompany weakness, vomiting, collapse, or impaired consciousness. The naturally affected dog developed ataxia before coma and residual weakness improved over approximately 33 hours (pqac-00000026, pqac-00000055). | Frequency not quantified; human descriptions and direct veterinary case evidence. | Ataxia |
| Seizures (neurologic manifestation) | Severe, usually acute manifestation of hyponatremic cerebral edema; may rapidly progress to respiratory compromise or coma. | Frequency not quantified specifically for water intoxication; recurrently reported in psychiatric and exercise-associated cases. | Seizure |
| Coma (neurologic manifestation) | Life-threatening acute manifestation. A dog became comatose after prolonged lake play but recovered without specific sodium therapy as brisk diuresis corrected the water excess (pqac-00000026, pqac-00000055). | Frequency not quantified; strong case-level evidence but no population denominator. | Coma |
| Cerebral edema / increased intracranial pressure (pathologic manifestation) | Develops rapidly when acute hypotonicity drives water into brain cells; can progress to herniation. Acute rat hyponatremia increased brain water from 78.3% in sham animals to 79.4–79.5%; severe mouse water loading caused brain-stem herniation after 23 ± 3 minutes (pqac-00000010, pqac-00000014). | Human frequency not quantified; mechanism strongly supported by animal experiments and severe clinical presentations. | Cerebral edema; Increased intracranial pressure |
| Hyponatremia with serum hypo-osmolality (laboratory abnormality) | Cardinal biochemical phenotype, often acute: serum Na <135 mmol/L with measured serum osmolality <275 mOsm/kg. A psychiatric-polydipsia case had Na 111 mmol/L and plasma osmolality 229 mOsm/kg; another mixed case had Na 115 mmol/L and 246 mOsm/kg (pqac-00000053, pqac-00000056). | Expected in clinically manifest dilutional water intoxication, but severity varies; no water-intoxication-specific frequency estimate. | Hyponatremia; Decreased serum osmolality |
| Dilute urine or inappropriately concentrated urine (laboratory abnormality) | In pure polydipsia with suppressed AVP, urine osmolality is generally ≤100 mOsm/kg: the 2023 Minhas case measured 55 mOsm/kg. Values >100 suggest AVP activity, impaired dilution, mixed disease, or timing effects; the 2023 Evanson case measured 280 mOsm/kg and had overlapping diagnostic features (pqac-00000053, pqac-00000056, pqac-00000057). | Pattern is mechanistically informative, not universal. The 2024 diagnostic algorithm supports <100 mOsm/kg for primary polydipsia/low-solute intake and >100 mOsm/kg for AVP-mediated states (pqac-00000027, pqac-00000042). | Decreased urine osmolality; Inappropriately concentrated urine |
| Rhabdomyolysis (complication) | Can accompany severe hyponatremia or overly rapid correction. In the Minhas case, Na rose from 111 to 128 mmol/L in 24 hours and creatine kinase increased from 3,356 to 131,072 IU/L; renal function remained preserved and the patient recovered (pqac-00000053). | Rare; frequency not quantified for water intoxication. Evidence consists chiefly of case reports. | Rhabdomyolysis; Increased serum creatine kinase |
| Osmotic demyelination syndrome (treatment complication) | Delayed neurologic complication principally associated with excessive correction of chronic or otherwise high-risk hyponatremia, rather than the untreated water load itself. Correction limits and rescue relowering are used preventively (pqac-00000045, pqac-00000046). | Rare and not quantified specifically for water intoxication; risk is highest with chronicity, alcoholism, malnutrition, liver disease, hypokalemia, or very low starting sodium. | Osmotic demyelination; Central pontine myelinolysis |


*Table: Phenotypes and complications are separated from predisposing behaviors and treatment-related injury, with onset, severity, and evidence limitations stated explicitly. Suggested ontology mappings are term labels only; no unverified HPO identifiers are assigned.*