Salt water gargle works for two reasons:
Gargling with salt water often provides temporary relief right away (though not always), but the real relief comes as your body’s own immune system more quickly heals the throat because you have simplified its job by using the gargle.
The gargle also helps to remove plaque on your teeth (which causes gum disease) and helps heal mouth sores–all while being isotonic and therefore not irritating to your tissues. A salt water rinse before bed is helpful if you do not have a tooth brush or toothpaste. See this NY Times article on the benefits of salt water gargle.
Combine and mix:
The water must not have chlorine in it, which could irritate your throat. So, do not use tap water unless your water comes from a well. Instead you can use use water from:
Chlorine is also a poison that weakens your immune system. It is added in small amounts to our drinking water to insure that the water is germ-free, but it is better to avoid it.
Dosage: Take as often as you wish, even every half hour–especially if it is washing out mucus from the back of your throat. You can use it daily as a preventative, and especially when you feel a cold coming on.
Put a little of the gargle in your mouth, tilt your head back and extend your tongue as you softly blow air up to agitate the gargle so it washes away the mucus.
Extending the tongue lets the gargle reach lower in your throat and cover a larger area. If you have never extended the tongue before, try it gently at first so you don’t accidentally breathe in the gargle. Gargling also cleans out the spaces at the back of the nose/above the throat where colds can linger.
How long do you gargle? Some sources say one to three minutes. Three minutes is a very long time. Most people gargle about ten seconds and twenty seconds seems like a long time. I would do at least 30 to 60 seconds of actual gargling when you are sick, doing it multiple times as needed. Keep going with fresh salt water until you are spitting out no mucus or gummy or discolored material. The gentle bubbling agitation of the salt water in your throat is what is removing the mucus. Repeat every few hours and continue for a day or so after you are feeling better.