Measure the desired amount of salt. For example, to make 0.01% saline, measure 1 gram of salt, which is equal to approximately 1 milliliter. Put the salt into a sterile beaker.
Measure distilled water into a dropper or syringe. For every gram of salt, subtract 1 milliliter of water. For example, mix 1 gram of salt with 99 milliliters of water. For 2 grams of salt, use 98 milliliters of water. Add the water to the beaker.
Mix the water and salt, ensuring that the salt is completely dissolved and that none clings to the sides of the beaker.
Pour the prepared saline into a sterile storage container with a tight lid. Saline should be kept in a cool, dry place out of direct sunlight. Do not refrigerate saline, as it is to be used at room temperature.