Saltwater is a solution created when salt dissolves into water. This mixture ranges from a weak solution made in a kitchen cup to the vast, complex oceans. Understanding how to make saltwater depends on the intended purpose, as the concentration and purity determine its safety and efficacy. For most practical applications, the process involves combining common table salt with purified water to achieve a specific, controlled ratio.
The Science of Dissolving Salt
The ability of salt to dissolve in water is rooted in the unique structure of the water molecule. Water is a polar molecule, meaning it has a slight positive charge on the hydrogen atoms and a slight negative charge on the oxygen atom. This electrical asymmetry allows water to interact strongly with ionic compounds like sodium chloride, or table salt.
Salt crystals are held together by ionic bonds between positively charged sodium ions and negatively charged chloride ions. When salt is introduced to water, the polar water molecules surround these ions, pulling the crystal apart in a process called dissociation. The oxygen side of the water molecule attracts the sodium ions, while the hydrogen side attracts the chloride ions, separating the salt into its individual components.
This process continues until the solution reaches its saturation point, where the water can no longer dissolve any more salt. The speed at which salt dissolves can be increased by raising the water temperature, as warmer water molecules move faster and collide with the salt crystals more frequently. The final amount of salt that can dissolve is a fixed property of the solution at a given temperature.
Creating Safe Saline Solutions for Home Use
Creating a safe saline solution for purposes like gargling or nasal rinsing requires careful attention to concentration and purity. The goal is typically an isotonic solution, which matches the natural salt concentration of the human body’s tears and blood, about 0.9% sodium chloride. This concentration prevents irritation or damage to delicate mucous membranes.
To achieve this 0.9% ratio, a common household recipe calls for mixing one-half teaspoon of non-iodized salt into one cup of water. Non-iodized salt must be used, as the additives in iodized salt can cause irritation in nasal passages or open wounds. The water must also be sterile, meaning it should be distilled or boiled for 15 minutes and then cooled before mixing.
Solutions with a higher salt content, known as hypertonic solutions, are sometimes used to draw fluid out of tissues, such as to relieve severe congestion. The use of sterile equipment and proper storage are paramount for any homemade saline solution. To prevent bacterial growth, homemade solutions should be discarded after 24 hours if made with boiled tap water, even when refrigerated.
Why Seawater is Different from Homemade Saltwater
Natural seawater differs drastically from a safe homemade saline solution in both concentration and chemical composition. The average ocean has a salinity of approximately 3.5%, containing about 35 grams of dissolved salt for every liter of water. This concentration is nearly four times higher than the 0.9% isotonic solution recommended for home use.
This high concentration means that seawater is significantly hypertonic compared to the fluids inside human cells. When consumed, the body attempts to balance the excess salt through a natural process called osmosis. Water is pulled out of the body’s cells and into the bloodstream to dilute the high salt load, leading rapidly to severe dehydration.
Seawater contains far more than just sodium chloride, though these two ions make up over 90% of the dissolved solids. Ocean water also contains a complex mixture of other ions, including magnesium, sulfate, calcium, and potassium, as well as various contaminants. These minerals and impurities make seawater unsuitable and unsafe for consumption or sensitive medical applications.