Is bacteriostatic water the same as sterile water?

No — sterile water is preservative-free and intended for single use.

Can bacteriostatic water be used to reconstitute peptides?

It is a common diluent in research handling of lyophilised peptides.

Bacteriostatic Water

What Is Bacteriostatic Water?

Reviewed by our laboratory team · Last updated 2026-07-03

Bacteriostatic water is sterile water containing 0.9% benzyl alcohol as a bacteriostatic preservative. The benzyl alcohol inhibits bacterial growth after the vial's initial puncture, making the same vial suitable for repeated withdrawal in research handling. It is not the same as plain sterile water.

Key facts

Composition: Sterile water + 0.9% benzyl alcohol
Purpose: Bacteriostatic preservation for multi-puncture use
Typical presentation: 10 mL or 30 mL vial

Why the benzyl alcohol

Benzyl alcohol at 0.9% inhibits bacterial growth in the vial after initial puncture. Without it, any organisms introduced by needle puncture could multiply between uses.

Extended research context

The Bacteriostatic Water deep dive

Deep dive: what makes water 'bacteriostatic'

Bacteriostatic water for injection is sterile water preserved with 0.9% benzyl alcohol. The benzyl alcohol disrupts bacterial cell membranes at low concentration, preventing microbial growth once the vial has been broached. That's why BAC water can be re-entered up to about 28 days after first use — sterile water cannot, because it has no preservative to inhibit contamination.

When to use BAC water vs sterile water in peptide research

BAC water is the default for reconstituting research peptides because researchers typically draw from the same vial across multiple sessions. Sterile water is appropriate only for single-use reconstitution or where benzyl alcohol would interfere with a downstream assay (rare, but possible in some cell-culture models sensitive to preservatives).

Compatibility and interactions

Benzyl alcohol is generally inert against most research peptides. The main exceptions are peptides with free thiols or highly reactive residues where the preservative could theoretically react — check the peptide's stability data. For 99% of research peptide handling, BAC water is the correct default.

Research applications

▸Reconstitution of lyophilised research peptides
▸Preparation of stock solutions for aliquoting
▸Diluent in analytical HPLC sample prep (where preservative is acceptable)
▸Reference solvent for peptide-stability studies
▸Teaching material for aseptic-technique training

Handling checklist

✓Store vial at room temperature (15–25 °C), out of direct sunlight
✓Use within 28 days of first puncture
✓Swab the septum with 70% isopropyl alcohol before each draw
✓Never share a BAC water vial across incompatible peptide chemistries
✓Discard the vial if cloudy, discoloured, or past the 28-day window

Common research-handling mistakes

Learnt from thousands of researcher orders across our UK labs.

✗ Using tap or distilled water instead of BAC

Fix: Only bacteriostatic or sterile WFI is appropriate — tap water contains microbes and minerals.

✗ Re-using a vial past 28 days

Fix: Even preserved, contamination risk rises; discard on the 28-day mark.

✗ Assuming BAC water is medicine-grade

Fix: It is a laboratory solvent when supplied for research; do not administer to humans.

Continue researching

Peer-reviewed guides, comparators and matched reference materials.

Frequently asked questions

Is bacteriostatic water the same as sterile water?: No — sterile water is preservative-free and intended for single use.
Can bacteriostatic water be used to reconstitute peptides?: It is a common diluent in research handling of lyophilised peptides.

Primary sources & clinical trials

Peer-reviewed research and registered trials from PubMed, ClinicalTrials.gov, PubChem, FDA and NIH. All links open in a new tab (external, rel="nofollow").

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