# Bacteriostatic Water (BAC Water) — Complete FAQ

Source: https://www.trackpep.com/blog/bac-water-faq

> Educational information only. Not medical advice, and not a dosing recommendation. TrackPep records what you enter and converts a dose you were prescribed into a syringe reading; it never decides a dose for you. Talk to a licensed clinician.

What BAC water is, why it's different from sterile water, how to store it, and answers to the questions people ask the most.

<Disclaimer />

**Bacteriostatic water** — usually called BAC water — is one of those background supplies that everyone tracking peptides relies on but few people understand. This FAQ answers the questions that come up most often.

## What is BAC water?

BAC water is **sterile water for injection with 0.9% benzyl alcohol added as a preservative**. The benzyl alcohol inhibits bacterial and fungal growth, which is what lets you draw from the same vial multiple times over a period of weeks without contaminating the solution.

## How is it different from "sterile water for injection"?

Plain sterile water for injection (SWFI) has no preservative. Once you puncture the seal, it's typically used within a few hours. BAC water buys you **~28 days** of multi-use shelf life once opened.

| | BAC water | Sterile water (SWFI) |
|---|---|---|
| Preservative | Benzyl alcohol 0.9% | None |
| Multi-use? | Yes (~28 days) | No (single-use) |

## Storage

- Unopened: room temperature, out of direct sunlight.
- Opened: refrigerate; ~28 days from first puncture.
- Label the vial with the date of first puncture.

<Callout>Do not freeze. Discard if you see particles, cloudiness, or discoloration.</Callout>

## Is BAC water safe for everyone?

Two specific cautions: **neonates and infants** should not receive benzyl alcohol-containing preparations, and **allergies to benzyl alcohol** are rare but real.

## How much should I use per vial?

Pick a BAC volume that puts your typical dose between **10 and 50 units** on a U-100 syringe. See [the reconstitution calculator guide](/blog/peptide-reconstitution-calculator-guide).

## Can I reuse one BAC vial across peptide vials?

Yes — that's its purpose. Aseptic technique (alcohol-swab the rubber stopper, fresh needle for each draw) is what matters.

## Common mistakes

- Drawing from a punctured vial after 28 days.
- Mixing with sterile water without recalculating concentration.
- Storing in the freezer.
- Cross-contaminating the rubber stopper.

<FAQ>
  <div>
    <dt>**Does BAC water expire on the shelf?**</dt>
    <dd>Unopened vials typically expire 18–24 months from manufacture. Check the label.</dd>
  </div>
  <div>
    <dt>**Is 0.9% benzyl alcohol the same as 0.9% saline?**</dt>
    <dd>No. Different molecule, different purpose.</dd>
  </div>
</FAQ>

---

*Informational only. Not medical advice.*