💧 Bacteriostatic water — what it is & why it matters
Almost every peptide ships as a dry powder you have to mix with liquid before you can dose it. What you mix it with — and how you handle it after — is a big part of doing this safely. The standard choice is bacteriostatic water.
Bacteriostatic water ("BAC water") is sterile water with 0.9% benzyl alcohol added as a preservative. The benzyl alcohol is the whole point: it holds back the growth of bacteria, so you can puncture the vial and draw from it many times over days or weeks without the solution spoiling.
Plain sterile water and saline have no preservative. They're fine for a single use, but once you've reconstituted a peptide you'll be drawing from that vial repeatedly — which is exactly where a preservative matters.
⭐ Why it matters
Multi-use safety. A 5–10 mg peptide vial often holds 10–30 doses. Bacteriostatic water keeps that vial usable for ~weeks instead of hours.
It's what dose math assumes. The volume of water you add sets the concentration, which sets how far you draw the syringe. The calculator works this out for you.
It reduces infection risk — the most realistic real-world harm here isn't the peptide, it's a contaminated vial or injection. A preservative plus sterile technique is your defense.
↔️ Bacteriostatic vs other diluents
Diluent
Preservative?
Best for
Bacteriostatic water
Yes (0.9% benzyl alcohol)
The default for multi-dose peptide vials. Lasts ~28 days refrigerated.
Sterile water for injection
No
Single-use only; use within a day or two. Use if you can't tolerate benzyl alcohol.
0.9% sodium chloride (saline)
No (unless "bacteriostatic saline")
Sometimes used for IV/IM or for peptides that prefer it. No preservative unless labeled bacteriostatic.
Never use tap water, distilled water from the store, or "drinking water." They are not sterile and are not safe to inject.
💉 How much do I add?
There's no single "right" amount — it's a trade-off. More water = more dilute, which makes each dose a larger, easier-to-measure draw (good if your dose is tiny). Less water = more concentrated, a smaller draw. Most small vials physically hold up to about 3 mL.
You don't have to guess: pick your peptide in the calculator and it sets the water for you, aiming for an easy ~10-unit draw on a standard insulin syringe.
🧊 Sterility & storage — the rules that keep you safe
Refrigerate after mixing — 36–46 °F (2–8 °C). Reconstituted peptide is fragile.
Roughly 28 days. The benzyl alcohol keeps a reconstituted vial usable for about a month. After that, discard it — the preservative's protection fades.
Don't freeze reconstituted solution, and keep it out of direct light.
Swab the stopper with alcohol before every single draw, and never reuse or share needles.
When in doubt, throw it out. Cloudiness, floating particles, or a color change means it's done.
Benzyl alcohol allergy is rare but real — if you react, switch to plain sterile water and use the vial up quickly.
Benzyl alcohol is not recommended for newborns and is best avoided in large repeated volumes during pregnancy — not a concern at normal peptide draw volumes, but worth knowing.
Bacteriostatic water is for reconstituting and injecting, not for drinking or IV fluid replacement.
🧮 Ready to reconstitute?
The calculator works out exactly how much bacteriostatic water to add and how far to draw the syringe.
See something off, or want a peptide added? If you notice anything wrong, incorrect, or missing — a peptide you'd like
us to add research for, or a feature that isn't working the way it should — please tell us at
info@peptide-dose.com. This is a community harm-reduction tool and we want it to be accurate.