Yes, pure water is hypotonic.
Understanding Hypotonic Solutions
A hypotonic solution has a lower concentration of solutes (dissolved substances) compared to another solution. In the context of cells, a hypotonic solution has a lower concentration of solutes than the fluid inside the cell. This difference in solute concentration drives osmosis—the movement of water across a semipermeable membrane from an area of high water concentration (low solute concentration) to an area of low water concentration (high solute concentration).
Pure water, lacking any solutes, represents the ultimate hypotonic solution relative to most biological fluids. When a cell is placed in pure water, water rushes into the cell to equalize the solute concentrations, potentially causing the cell to swell and even burst (lyse).
Several sources confirm this:
- [Reference 1]: "In this situation, pure water is a hypotonic solution."
- [Reference 8]: "Sterile water is hypotonic (0 mOsm/L)."
- [Reference 6]: "Water for injection, which is hypotonic, is indicated for dissolving or diluting injectable therapeutic substances for parenteral..."
Practical Implications
The hypotonic nature of pure water has significant implications in various fields:
- Medicine: Intravenous (IV) administration of pure water is dangerous because it can cause hemolysis (rupture of red blood cells). Solutions used for IV fluids are usually isotonic to prevent such damage.
- Biology: Researchers use hypotonic solutions in experiments to study cellular processes affected by water movement into cells.
- Sports: Hypotonic sports drinks are formulated to replenish fluids lost during exercise more effectively than plain water in some cases, since it provides both water and electrolytes.
Understanding tonicity—the relative concentration of solutes in a solution compared to another—is crucial in many scientific and medical applications.
