Sterile water is water that has no microorganisms living within it. As it cannot transfer pathogens, it is used mainly in the medical setting. Sterile water, though sometimes distilled, is not the same thing as distilled water. As some microorganisms can survive at high temperatures, simply boiling water may not be enough to sterilize it. Special, but not uncommon, equipment is required if one wishes to sterilize water.
This kind of water is free of all microbial life. As sterilized water does not contain the same amount of dissolved salt as the human body, overhydration would occur if a physician used the water as an irrigation fluid during surgery or other invasive medical procedures. The value of sterile water is its ability to act as a solvent in many pharmacological compounds that physicians will eventually inject into patients. The water is also a tool in helping physicians clean wounds without putting patients at risk for infection.
Water that is sterile plays a large role in medical research. In many cases, water is necessary to study microorganisms. Using this water is required in these and other experiments as normal or even distilled water may introduce outside bacteria into the experiment. This contamination would invalidate all test results and put other experiments in the same laboratory at risk. Therefore, sterilized water is the only acceptable water for laboratory research.
Sterilized and distilled water are two different things. Distilled water lacks all salt and other mineral compounds. As it can never leave mineral deposits on surfaces, distilled water has many uses in industrial settings where water cooling is necessary. Depending on the need, it is possible to create water that is both sterilized and distilled. The process of distillation must come before or after sterilization.
The most common method of sterilizing water for personal use is boiling it for 20 to 30 minutes. This practice kills the majority of microorganisms. Yet some microorganisms, especially those that can cause life-threatening infections, can survive in boiling water. A different process is needed to make water truly sterile.
In order to make medical grade sterile water at home, a pressure cooker is required. The use of pressure forces the temperature of the water to rise higher than its natural boiling point. This temperature increase kills any lingering microorganisms. The water that comes out of this process is medical grade and acceptable to use in medical applications.