Bacteriostatic Water vs Sterile Water

Instructor: Adrianne Baron

Adrianne has taught high school and college biology and has a master's degree in cancer biology.

We are going to learn some information about sterile and bacteriostatic water. We will go through the differences between the two types of water as well as concerns in regards of their use.


You are at the doctor's office waiting for the doctor to finish writing a prescription for the illness that has plagued your body for the last week. The nurse enters the room to hand you the much anticipated prescription and give you instructions on how to take the medication. You are expecting something simple like a pill to take once every so many hours. What you receive is a prescription for a drug that has to be mixed with water and then injected into your body. You weren't prepared for that.

Water from the faucet is not safe to inject into the body

You begin to think about the different reports you've seen in regards to contaminated drinking water. You don't drink the water that comes from the tap, you buy bottled water. At times you aren't even sure how safe that is. So what water are you going to use to inject this medicine into your body?

There are two main choices for water to use to inject medications into your body. Which of the two you use is dependent upon whether or not you need to use the water once or more than once.

Sterile Water

The first option that you may use for mixing your medication is sterile water. This is water that doesn't have any microorganisms, also called 'microbes', living in it. By microorganisms, I mean viruses, bacteria, fungi, etc. Sterile water is designed to be used only one time, so the vial will have enough in it for one use.

It is important that you only use it one time in order to avoid contaminating the water with microbes. Just remember, sterile water is only sterile until it is opened and exposed to the air or something is inserted into to it.

Sterile water comes in single dose vials to mix with medication
Picture of dose size vial and syringe

While it is safe to mix the drugs in sterile water for injection, it is not a very good idea to inject sterile water into your veins since that will upset your body's balance and may cause your blood cells to split which we refer to as hemolysis_. But for mixing drugs that have to be taken every day, it is safe to use on a regular basis.

Bacteriostatic Water

Your other option is bacteriostatic water. In this case we are still dealing with the sterile water we just described, but it also contains benzyl alcohol which prevents the growth of bacteria in the vial. The alcohol or any other agent that prevents bacterial growth is known as a bacteriostat hence the name, bacteriostatic water. Makes sense now, right?

Bacteriostatic water comes in a larger vial to be used more than once
Picture of a larger vial and syringe

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