Can You Drink Seawater? No—It’s Dangerously Dehydrating

Absolutely not. Seawater contains ~3.5% salt (35 g/L). Human kidneys can only produce urine up to ~2% salt. Drinking seawater forces the body to excrete more water than consumed to eliminate the salt load → net dehydration.

Physiological Cascade

1. Salt intake ↑ → blood osmolarity ↑.
2. Cells shrink (water leaves via osmosis).
3. Thirst center triggered → but drinking more seawater worsens cycle.
4. Kidneys overwork → tubular damage, acute kidney injury.
5. Neurological: confusion, seizures, coma (hypernatremia).
6. Cardiovascular: volume depletion → shock.

Survival Context

• Life rafts: Never drink seawater. Use solar stills, rain catchment, reverse-osmosis hand pumps (e.g., Katadyn Survivor 06).
• Historical: La Balsa raft (1970) survived 161 days on rain/fish fluid only.
• Animals: Seabirds (salt glands), marine mammals (efficient kidneys), some fish (osmoregulation) can; humans cannot.

Desalination

Modern RO membranes (SWRO) produce potable water at ~3–4 kWh/m³. Shipboard and coastal plants rely on this—not human physiology.

Bottom line: seawater is a toxin for humans. Don’t test it.