1. What BAC water is
Bacteriostatic water (BAC water) is sterile water for injection that contains 0.9% benzyl alcohol as a preservative. The benzyl alcohol inhibits bacterial growth, which means the vial can be safely re-entered multiple times with a needle over an extended period.
It is the standard diluent for reconstituting lyophilised (freeze-dried) research peptides. The 10 mL vials sold on this site are the same pharmaceutical-grade BAC water used in clinical settings.
2. BAC water vs. sterile water
| BAC Water (0.9% benzyl alcohol) | Sterile Water for Injection | |
|---|---|---|
| Preservative | Yes — 0.9% benzyl alcohol | None |
| Multi-dose safe | Yes — up to 28 days after first puncture | No — single use only |
| Can be re-entered | Yes | No — discard after first draw |
| Shelf life (opened) | 28 days refrigerated | Use immediately |
| Suitable for peptides | Yes — the correct choice | Only if using the entire vial in one injection |
| Pain on injection | Negligible at subcutaneous volumes | Negligible |
3. How much BAC water to add
The most common convention is 2 mL of BAC water per vial regardless of vial size. This gives a predictable concentration that the reconstitution calculator uses by default.
| Vial size | BAC water added | Resulting concentration | Notes |
|---|---|---|---|
| 5 mg | 2 mL | 2,500 mcg/mL | Standard — easiest to dose |
| 10 mg | 2 mL | 5,000 mcg/mL | Concentrated — small volumes per dose |
| 10 mg | 4 mL | 2,500 mcg/mL | Diluted — easier to read syringe |
| 20 mg | 4 mL | 5,000 mcg/mL | Standard for larger vials |
There is no single “right” amount — the reconstitution calculator handles any combination. The reason 2 mL is the default is that it produces a concentration where typical peptide doses (250–500 mcg) land on easy-to-read syringe markings (10–20 units).
4. How BAC water volume affects your dose
The amount of BAC water you add directly determines the concentration, which directly determines how many units you draw. Always enter the actual volume you added into the reconstitution calculator — not an assumption.
Example with a 5 mg vial:
With 1 mL BAC water: 5000 mcg/mL → 250 mcg dose = 5 units
With 2 mL BAC water: 2500 mcg/mL → 250 mcg dose = 10 units
With 4 mL BAC water: 1250 mcg/mL → 250 mcg dose = 20 units
The dose (250 mcg) is the same in all three cases — the concentration just determines how many units you draw to deliver it.
5. Shelf life after reconstitution
| Storage method | Expected stability |
|---|---|
| Refrigerator (2–8°C) | Up to 28 days for most peptides reconstituted in BAC water |
| Freezer (−20°C) | Not needed with BAC water; can degrade some peptides with repeated freeze-thaw |
| Room temperature | Not recommended — significantly shortens stability |
| Light exposure | Avoid — some peptides (especially melanocortin peptides) are light-sensitive |
6. Where to get BAC water
Capital Peptides sells pharmaceutical-grade BAC water (10 mL vials, 0.9% benzyl alcohol) in the supplies section. Each vial is sufficient for multiple reconstitutions.
Do not source BAC water from unknown online suppliers. Contaminated diluent is a real risk — use pharmaceutical-grade water from a verified supplier.