Bacteriostatic Water Guide
Bacteriostatic water is the standard solvent used to reconstitute lyophilized research peptides. This guide explains what it is, why it's used, how much to use, and how to store solutions after reconstitution.
What is bacteriostatic water?
Bacteriostatic water (often abbreviated "BAC water") is sterile water that contains 0.9% benzyl alcohol as a preservative. The benzyl alcohol inhibits the growth of bacteria, which allows a reconstituted solution to be used over multiple withdrawals across a period of days to weeks rather than a single use.
It differs from other common waters used in the lab:
- Bacteriostatic water — sterile + 0.9% benzyl alcohol. Multi-use; the preservative limits microbial growth between withdrawals.
- Sterile water for injection — sterile, no preservative. Single-use; once opened it should not be stored.
- Distilled or deionized water — purified but not necessarily sterile. Not appropriate for reconstitution.
Why benzyl alcohol matters
The 0.9% benzyl alcohol is what makes the water "bacteriostatic" — it suppresses bacterial replication so a reconstituted vial remains usable across a working period. Without a preservative, any introduced microorganisms could multiply in the solution between uses. This is the practical reason BAC water is preferred over plain sterile water for research that involves more than a single withdrawal.
How much to use
The volume of bacteriostatic water you add determines the final concentration of your solution. The relationship is simple:
Volume of BAC water (mL) = peptide mass (mg) ÷ desired concentration (mg/mL)
Worked examples:
- A 5 mg vial + 2 mL BAC water → 2.5 mg/mL
- A 5 mg vial + 1 mL BAC water → 5 mg/mL
- A 10 mg vial + 2 mL BAC water → 5 mg/mL
More water = lower concentration per unit volume (and a larger, easier-to-measure withdrawal). Less water = higher concentration (and a smaller withdrawal). The choice depends on the resolution of measurement your protocol requires.
Reconstitution procedure
- Bring both the lyophilized vial and the BAC water to room temperature.
- Wipe both rubber septa with an alcohol pad.
- Draw the calculated volume of BAC water into a sterile syringe.
- Tilt the peptide vial and inject the water slowly against the inside wall of the vial — not directly onto the powder.
- Let the powder dissolve on its own. Swirl gently if needed. Do not shake — aggressive agitation can denature some peptides.
- The finished solution should be clear with no visible particulates. Discard any solution that appears cloudy or has precipitate.
Storing solutions after reconstitution
Reconstituted solutions are less stable than the dry lyophilized powder. General guidance:
- Refrigerated (2–8°C): Most reconstituted peptides remain usable for 2–4 weeks. The benzyl alcohol in BAC water is what makes this multi-week window possible.
- Frozen (−20°C): For longer storage. Aliquot into single-use portions before freezing and avoid repeated freeze-thaw cycles.
Always defer to compound-specific stability data on the product page when it differs from these general guidelines.
Where to get bacteriostatic water
Bacteriostatic water is a separate research consumable. Rewerk ships lyophilized peptides; you supply the BAC water and sterile syringes appropriate to your protocol.
Research use only
All reconstitution guidance on this page is intended for in vitro laboratory research by qualified researchers. It is not instruction for human or animal administration. Rewerk products are not drugs, biologics, food, cosmetics, or dietary supplements.