April, 2015:
Kids, did you know that a "saline" solution refers to a salt solution, which you can prepare yourself using readily available materials. The solution can be used as a disinfectant, sterile rinse, or for labwork (although not for contact lenses - see a note below about that). This recipe is for a salt solution that is the same concentration as body fluids. The salt in saline solution discourages bacterial growth while rinsing away contaminants. Because the salt composition is similar to that of the body, it causes less tissue damage than you would get from pure water.
Technically, a saline solution results whenever you mix any salt with water. The easiest saline solution consists of sodium chloride (table salt) in water. For some purposes, it's fine to use a freshly mixed solution. In other cases, you'll want to sterilize the solution. Keep the purpose in mind when you mix the solution. If, for example, you are simply rinsing your mouth with saline solution as a dental rinse, you can mix any amount of table salt with warm water and call it good. If, however, you are cleaning a wound, for example, it's important to use pure ingredients and maintain sterile conditions.
You can use pure table salt from the grocery store. It's best to use uniodized salt, which does not have added iodine. Avoid using rock salt (halite) or sea salt; even though these are primarily sodium chloride, there are additional types of salts and other contaminants may cause problems for some purposes. Use distilled water or reverse osmosis purified water rather ordinary tap water. You want 9 grams of salt per liter of water or 1 teaspoon of salt per cup (8 fluid ounces) of water.
As a mouth rinse, you can simply dissolve the salt into very warm water. You may even wish to add a teaspoon of baking soda (sodium bicarbonate).
For a sterile solution, dissolve the salt in boiling water. Keep the solution sterile by placing a lid over the container so that no microorganisms get into the liquid or air space as the solution cools. You can dispense the sterile solution into sterile containers. Have an adult partner sterilize containers either by boiling them or by treating them with a disinfecting solution, such as the type sold for home brewing or making wine. It's a good idea to label the container with the date and to discard it if the solution is not used within a few days. This solution could be used for treating new piercings or for wound care. It's important to avoid contaminating the liquid, so ideally make just as much solution as you need at a time, allow it to cool, and discard leftover liquid. The sterile solution will remain suitable for lab use for several days in its sealed container, but you should expect some degree of contamination once it is opened.
Note: Although it is the proper salinity, this solution is not suitable for contact lenses. Commercial contact lens solution contains buffers that help protect your eyes, plus the solution includes agents to help keep the liquid sterile.
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References:
Anne Marie Helmenstine: http://chemistry.about.com/od/labrecipes/a/How-To-Make-Saline-Solution.htm
