Learn how to make bac water for peptides with sterile technique, 0.9% benzyl alcohol ratios, storage tips, and why most researchers buy it instead.
Bacteriostatic water — usually called "bac water" — is sterile water with 0.9% benzyl alcohol added as a preservative, and it is the standard diluent for dissolving powdered peptides. You can technically make it yourself by combining USP-grade benzyl alcohol with Sterile Water for Injection and filtering the result through a 0.22-micron filter. Most people should not, though, because a home batch cannot be verified as sterile, correctly dosed, or stable, and pharmaceutical-grade bac water is inexpensive and easy to buy.
What Bac Water Is and Why Peptides Need It
Peptides often ship as a lyophilized (freeze-dried) powder that has to be dissolved before use. Bac water for peptides does two jobs at once: it rehydrates the powder, and the benzyl alcohol it contains slows bacterial growth so a vial can be entered more than once.
Plain sterile water has no preservative. Once you puncture a vial of sterile water, bacteria can multiply inside it, which is why those vials are meant for a single session. Benzyl alcohol at 0.9% is bacteriostatic — it does not sterilize a contaminated vial, but it does inhibit growth in a properly handled one.
How to Make Bac Water at Home
The core recipe for how to make bac water is simple: 0.9% benzyl alcohol by volume in sterile water. Everything difficult about the process is in the sterile technique, not the chemistry.
- Work in a still-air environment. A laminar flow hood is ideal; a still-air box with no drafts and no foot traffic is the realistic minimum.
- Start with Sterile Water for Injection, USP, from a sealed pharmacy-grade container — not bottled drinking water or grocery-store distilled water.
- Add 0.9 mL of USP-grade benzyl alcohol for every 100 mL of sterile water.
- Draw the mixture through a 0.22-micron sterile syringe filter into a sterile glass vial with a rubber stopper.
- Label the vial with the date it was made and the concentration, then store it away from light.
A 0.22-micron filter removes bacteria, but it does not remove bacterial endotoxins, viruses, or chemical contaminants that were already in your starting materials. The filter also cannot tell you whether your finished vial is actually sterile.
Equipment, Costs, and the Real Risks of DIY Bac Water
Making your own supply requires more than a bottle of preservative and a syringe. Each item below is a point where contamination or dosing error can enter the process.
| Item | Role | What to look for |
|---|---|---|
| Sterile Water for Injection, USP | Base solution | Sealed, pharmacy grade, unexpired |
| Benzyl alcohol, USP | Preservative at 0.9% | Pharmaceutical grade, not industrial grade |
| 0.22-micron syringe filter | Removes bacteria | Sterile, single use, not for endotoxin removal |
| Sterile glass vial and stopper | Final container | Sealed, sterile, properly crimped |
| Laminar flow hood or still-air box | Reduces airborne particles | Clean, dedicated, not a kitchen counter |
The biggest risk is invisible contamination. A cloudy or particle-filled vial is obvious, but a vial with low-level bacterial growth looks perfectly clear. Sterility testing requires an incubator and time, which is why commercial manufacturers test every batch and home producers cannot.
Benzyl alcohol is not inert either. Some people are sensitive to it, and it is contraindicated for newborns. Bacteriostatic water is a diluent, not a product intended for direct injection on its own.
Buying Bac Water vs. Making It
For most people, the practical answer is to buy it. Pharmaceutical-grade bacteriostatic water is sold in 30 mL vials by medical supply companies and compounding pharmacies, usually for a few dollars each.
| Factor | Homemade Bac Water | Commercial USP Bac Water |
|---|---|---|
| Sterility assurance | None; untested | Batch tested by manufacturer |
| Cost per 30 mL | Low materials cost, high equipment cost | A few dollars |
| Shelf life | Unknown | Expiration date printed on the label |
| Time required | Hours, plus supplies sourcing | Order online, arrives in days |
| Documentation | None | Lot number, USP labeling, expiry |
When you research where to buy bac water for peptides, check the label: it should read "Bacteriostatic Water for Injection, USP," list 0.9% benzyl alcohol, include a lot number and expiration date, and come from a licensed supplier. Unlabeled vials or bottles marked only "research grade" with no manufacturer name are a gamble.
How Much Bac Water to Reconstitute Peptides
The math for how much bac water to reconstitute peptides depends on the vial size and the concentration you want. More water gives a weaker concentration and a larger volume per measurement; less water gives a stronger concentration that can be harder to measure accurately on a small syringe.
| Peptide Vial | Bac Water Added | Final Concentration |
|---|---|---|
| 5 mg | 1 mL | 5 mg/mL |
| 5 mg | 2.5 mL | 2 mg/mL |
| 10 mg | 1 mL | 10 mg/mL |
| 10 mg | 2 mL | 5 mg/mL |
| 10 mg | 5 mL | 2 mg/mL |
Learning how to mix peptides with bac water takes about two minutes. Swab both stoppers with alcohol and let them dry, inject the water slowly down the inside wall of the vial instead of directly onto the powder, and swirl gently until everything dissolves. Shaking creates foam and can damage fragile peptides, so that is the step to slow down on.
Storage, Safety, and Legal Context
Store reconstituted vials in the refrigerator, roughly 2°C to 8°C (36°F to 46°F), and keep them out of light. Most preservative-based diluents are labeled for about 28 days after the first puncture, though individual peptide stability varies widely and some compounds degrade much faster.
Discard any vial that turns cloudy, changes color, or shows visible particles, and never share a vial or syringe with another person. Making bac water at home is feasible in a real lab setting, but the sterility risk almost always outweighs the savings for a product that costs a few dollars per vial.
In the United States, most peptides sold online are not FDA-approved for human use, and bacteriostatic water is a prescription-labeled diluent rather than an approved standalone injectable. Anyone considering peptide use should talk with a licensed healthcare professional or pharmacist instead of relying on forum recipes.
Frequently Asked Questions
Can you make bacteriostatic water at home?
Technically, yes: 0.9% USP benzyl alcohol in Sterile Water for Injection, filtered through a 0.22-micron filter, matches the commercial formula. The problem is verification — a home setup cannot test the finished vial for bacteria or endotoxins, so contamination can go completely unnoticed. For most people, buying USP-grade bac water is safer and cheaper than building a sterile process.
How long does bac water last after opening?
A punctured vial of bacteriostatic water is generally treated as usable for about 28 days when handled with sterile technique and stored away from light. An unopened vial is good until the expiration date printed on the label. Discard it sooner if the liquid looks cloudy or contains particles.
Is bac water the same as sterile water?
No. Sterile water for injection contains no preservative and is meant for single use, because bacteria can multiply in it after the first puncture. Bacteriostatic water contains 0.9% benzyl alcohol, which inhibits bacterial growth so the same vial can be entered multiple times. That difference is exactly why bac water is used for multi-use peptide vials.
This page provides educational research information and does not replace medical advice, diagnosis, or treatment.