Bacteriostatic water vs sterile water.
Bacteriostatic water and sterile water both start as sterile water; the difference is one ingredient, 0.9% benzyl alcohol, and it decides whether a vial is single-use or can be opened again.
One preservative.
Sterile water contains nothing but water. Once its seal is broken there is nothing to stop microbes that get in from growing, so it is treated as single-use. Bacteriostatic water is sterile water with 0.9% benzyl alcohol, a preservative that suppresses bacterial growth, so the same vial can be entered more than once. (Bacteriostatic saline adds 0.9% sodium chloride; see bacteriostatic water vs saline.)
Studies that compared the two as diluents show the difference directly. In a 2005 study, a protein solution made with bacteriostatic water passed the USP antimicrobial effectiveness test while the same solution made with sterile water failed it, and a 2011 study found that protein samples made with bacteriostatic water met the USP growth-inhibition criteria in testing that ran up to 28 days.
The two at a glance.
| Bacteriostatic water | Sterile water | |
|---|---|---|
| Contents | Sterile water + 0.9% benzyl alcohol | Sterile water only |
| Preservative | Yes, suppresses bacterial growth | None |
| Vial use | Multiple entries | Single use, then discard |
| After opening | 28 days under USP practice, unless the label says otherwise | Use once |
| Typical lab role | Diluent for vials used over several sessions | Diluent when the whole vial is used at once |
How long does bacteriostatic water last?
A sealed vial lasts until the expiration date printed on it. Once the stopper has been punctured, standard pharmacy practice under USP chapter 797 gives a multiple-dose container 28 days unless the manufacturer specifies otherwise. Date the vial when you first open it. The full guide to how long bacteriostatic water lasts covers storage and when to discard a vial.
The preservative lowers risk; it does not remove it. A hospital survey found bacterial contamination in 5.6% of used multiple-dose vials, which is why vials are entered with clean technique and discarded on schedule.
Keeping it in spec.
Keep bacteriostatic water sealed at room temperature and away from light. Once a peptide has been dissolved in it, store the solution the way the peptide needs, usually refrigerated; the peptide storage guide covers that.
A tested lot, verifiable at the lab.
Helion's Bacteriostatic Water 3ml, lot 060226A, was tested by ILS Laboratories: benzyl alcohol 0.947% against a 0.8 to 1.0% specification, pH 6.9, 99.87% HPLC purity, identity confirmed and endotoxin at or below 0.05 EU/mL. The report is in the COA Portal with a link to ILS's own verification page. It is $8.99 and sold for laboratory research use only, to buyers 21 and over.
Specs and storage by compound.
Questions (5)
What is the difference between bacteriostatic water and sterile water?
Bacteriostatic water is sterile water with 0.9% benzyl alcohol, a preservative that suppresses bacterial growth so the vial can be entered more than once. Sterile water has no preservative and is single-use once opened.
How long does bacteriostatic water last after opening?
Under standard pharmacy practice (USP chapter 797), a multiple-dose vial is used for up to 28 days after it is first punctured, unless the manufacturer specifies otherwise. A sealed vial lasts until its printed expiration date.
Can sterile water be used instead of bacteriostatic water?
For a vial used all at once, yes. For a vial that will be entered several times, sterile water has no preservative, so bacteriostatic water is the standard laboratory choice.
How should bacteriostatic water be stored?
Sealed, at room temperature and away from light. Once a peptide is dissolved in it, store the solution as that peptide requires, usually refrigerated.
Is Helion's bacteriostatic water tested?
Yes. Lot 060226A was tested by ILS Laboratories: 0.947% benzyl alcohol, pH 6.9, 99.87% HPLC purity, identity confirmed and endotoxin at or below 0.05 EU/mL. The report can be checked on ILS's own portal.
Published studies (4)
- Alteplase as a catheter locking solution: in vitro evaluation of biochemical stability and antimicrobial properties
- In vitro stability and compatibility of tenecteplase in central venous access devices
- The prevalence of multidose vial contamination by aerobic bacteria in a major teaching hospital, Shiraz, Iran, 2006
- Final report on the safety assessment of Benzyl Alcohol, Benzoic Acid, and Sodium Benzoate
Citations from PubMed for reference. They describe the compound in the literature, not any Helion lot, and nothing here is guidance on use.