Bacteriostatic Water Quick Start
Bacteriostatic water is sterile water containing 0.9% benzyl alcohol as a preservative. The benzyl alcohol is what makes the vial multi-dose: it suppresses microbial growth, so the vial can be punctured repeatedly over weeks rather than discarded after one draw. It is the standard diluent for reconstituting lyophilized research peptides, and every reconstitution figure elsewhere on this site assumes it.
This guide is an educational research reference. It does not diagnose, treat, or prescribe, and is not medical advice. Consult a licensed clinician before considering any compound.
How Much To Add
The volume of bacteriostatic water added is a choice, not a fixed property of the peptide — it sets the concentration and therefore how many syringe units a given dose is. More water means a more dilute solution and a larger, easier-to-measure draw; less water means a smaller draw and more solution left in the vial for later. The peptide amount never changes.
| Vial content | BAC added | Concentration | Per U-100 unit |
|---|---|---|---|
| 10 mg | 2 mL | 5,000 mcg/mL | 50 mcg |
| 10 mg | 3 mL | 3,333 mcg/mL | 33.3 mcg |
| 30 mg | 3 mL | 10 mg/mL | 100 mcg |
| 40 mg | 3 mL | 13.3 mg/mL | 133 mcg |
| 70 mg | 3 mL | 23.3 mg/mL | 233 mcg |
| 100 mg | 3 mL | 33.3 mg/mL | 333 mcg |
| 1000 mg | 3 mL | 333 mg/mL | 3.33 mg |
Choosing a volume
| Consideration | Less water (e.g. 2 mL) | More water (e.g. 3 mL) |
|---|---|---|
| Draw size | Smaller — harder to measure precisely | Larger — easier to read on the barrel |
| Microgram doses | Can land below 5 units | Keeps small doses readable |
| Milligram doses | Keeps the draw under 1 mL | May exceed one syringe fill |
| Vial headroom | More room to spare | Most vials cap around 3 mL |
Most peptide vials will not hold much beyond 3 mL. Always confirm the vial's capacity before drawing a larger volume, and recalculate the concentration whenever the volume changes. The reconstitution calculator will do the arithmetic for any combination.
Reconstitution Steps
These are the same steps referenced on every lyophilized-peptide page on this site, collected here in one place.
- Inspect both vials. Confirm the peptide label and expected milligram amount, and that the powder looks dry and intact. Check that the bacteriostatic water is clear and unexpired.
- Wipe the stoppers. Use a fresh alcohol swab on both the bacteriostatic water and the peptide vial, and let them dry.
- Draw the chosen volume. Pull the volume decided above into the syringe — this is the number that sets every concentration figure downstream.
- Inject down the wall. Release the water slowly down the inside wall of the vial, not directly onto the powder. A hard stream can damage the peptide.
- Swirl, do not shake. Roll the vial gently between the palms until fully dissolved. Shaking causes foaming and can denature the peptide.
- Verify clarity. The solution should be clear and colorless, with the documented exception of GHK-Cu, which is blue. Discard anything cloudy or particulate.
- Label and refrigerate. Note the date and the volume added on the vial, then store the reconstituted peptide at 2–8 °C. The bacteriostatic water vial itself stays at room temperature.
Why Bacteriostatic, Not Plain Sterile Water
Plain sterile water is sterile only until the moment it is opened. Bacteriostatic water adds 0.9% benzyl alcohol, a preservative that inhibits the growth of most bacteria, so the vial tolerates repeated puncture over an extended period. For a peptide vial that will be drawn from daily for several weeks, that preservative is the entire point.
Multi-dose tolerance
Benzyl alcohol suppresses microbial growth between punctures, supporting repeated draws.
Peptide stability
The mildly acidic pH (4.5–7.0) suits most peptides in solution.
Standard reference
Published and community reconstitution figures generally assume bacteriostatic water, so results stay comparable.
Open question
Preservative compatibility is not established for every peptide; a small number are documented as preservative-sensitive.
When Not To Use It
Bacteriostatic water is the default diluent, not a universal one. The benzyl alcohol that makes it multi-dose is also what creates the exceptions below.
Neonatal contexts
Benzyl alcohol is contraindicated in newborns; this is the best-documented restriction on the preservative.
Benzyl alcohol sensitivity
Known hypersensitivity to the preservative rules it out; sterile water is the alternative.
Large cumulative volumes
Preservative load adds up across many millilitres, which is why the preserved form is intended for small multi-dose draws.
Preservative-sensitive peptides
A few compounds specify sterile water or a particular buffer — follow the label rather than the default.
Safety & Handling
Aseptic technique
Swab before every puncture and use a fresh needle each time; the preservative slows contamination, it does not reverse it.
Not an injectable on its own
It is a diluent. Plain water injected alone is hypotonic and is not how the reagent is used.
Puncture count
Stoppers degrade with repeated puncture; coring pushes rubber fragments into solution.
Quality-control risk
Verify sterility claims and expiry — a contaminated diluent compromises every vial reconstituted from it.
Storage
| State | Storage | Notes |
|---|---|---|
| Unopened | Room temperature | Protect from light; do not refrigerate or freeze. |
| Opened / punctured | Room temperature | Commonly referenced as ~28 days after first puncture; follow the label. |
| Appearance | Clear, colorless | Discard if cloudy, discolored, or particulate. |
| Reconstituted peptide | 2–8 °C | Once mixed, the peptide's storage rules apply — not the diluent's. |
Mistakes & Troubleshooting
- Forgot how much water was added. The concentration is unverifiable. Do not guess and dose from it.
- Solution foamed. Caused by shaking. Let it settle; swirl gently next time. Heavy foaming suggests the peptide was agitated too hard.
- Powder will not dissolve. Give it several minutes at room temperature with gentle rolling before concluding anything is wrong.
- Cloudy after mixing. Do not use it — discard and replace. Clear and colorless is the standard, with GHK-Cu's blue as the documented exception.
- Refrigerated the BAC water vial. Not harmful, but unnecessary; the diluent belongs at room temperature. The reconstituted peptide is what needs refrigerating.
- Used it on a pre-reconstituted pen vial. Pen vials arrive at their final 3 mL volume — adding water invalidates every dose figure for that vial.
Bacteriostatic Water vs Sterile Water vs Saline
| Feature | Bacteriostatic water | Sterile water | Bacteriostatic saline |
|---|---|---|---|
| Preservative | 0.9% benzyl alcohol | None | 0.9% benzyl alcohol |
| Solutes | None | None | 0.9% sodium chloride |
| Vial use | Multi-dose | Single use once opened | Multi-dose |
| Typical role | Default peptide diluent | Preservative-sensitive compounds | Where an isotonic diluent is specified |
Substituting one diluent for another does not change the milligram content of a vial, but it can change solution stability and how long a punctured vial remains usable. Follow the compound's own label where it specifies a diluent.
Frequently Asked Questions
What is bacteriostatic water?
Sterile water with 0.9% benzyl alcohol added as a preservative. The preservative inhibits microbial growth, which is what allows a vial to be punctured repeatedly instead of discarded after one use.
How much should I add to a vial?
It is a choice that sets the concentration, not a fixed value. 2 mL and 3 mL are the common references. 3 mL is the tidiest because it equals exactly 300 units on a U-100 syringe, making per-unit = vial mg ÷ 300 × 1000 mcg. See the volume table above.
Does the amount of water change the dose?
It changes the volume you draw, not the milligrams in the vial. More water means the same dose occupies more units on the syringe. Recalculate whenever you change the volume.
Can I use it with pre-reconstituted pen vials?
No. Pen vials ship already at 3 mL, so there is nothing to reconstitute. Adding water would dilute the solution and invalidate every dose figure published for it.
How long does it last once opened?
Commonly referenced as about 28 days after first puncture, stored at room temperature and protected from light. Follow the vial label, which is authoritative over any general figure.
Is this page medical advice?
No. It is an educational research reference and does not diagnose, treat, or prescribe. Consult a licensed clinician before considering any compound.
Formats & Sourcing
Bacteriostatic water is supplied as a 30 mL multi-dose vial — enough to reconstitute roughly ten 3 mL vials. It is the ancillary reagent assumed by every lyophilized-peptide protocol on this site; the pre-reconstituted pen-vial formats do not require it.
| Format | Supplied as |
|---|---|
| Multi-dose vial | 30 mL — sterile water USP + 0.9% benzyl alcohol |
Specification per the product listing: pH 4.5–7.0, sterility to USP <71>, stored at room temperature and protected from light. Confirm against the vial label.
Reference reagent for the protocols on this site:
View Bacteriostatic Water on Spyro Peptides →References
- United States Pharmacopeia. Bacteriostatic Water for Injection, USP monograph.
- United States Pharmacopeia. General Chapter <71>: Sterility Tests.
- US Food and Drug Administration. Benzyl alcohol and neonatal gasping syndrome — safety communication.
- Centers for Disease Control and Prevention. Safe injection practices: single- and multi-dose vials.
- Per-compound reconstitution figures are compiled on the individual protocol pages.