Bacteriostatic Water

Not a peptide, but the thing every peptide depends on

Bacteriostatic water is USP-grade sterile water with 0.9% benzyl alcohol added as a preservative. It is in this library because getting it wrong ruins everything downstream, and because the single most common way people waste a $70 vial is bad reconstitution.

Is bac water the same as sterile water?

No. Both are sterile water for injection, but bac water adds a preservative, benzyl alcohol, and comes in a multiple-dose vial. That is why one vial can be used for up to 28 days. Sterile water has no preservative and comes in single-dose vials, so a peptide mixed with it is used within 24 hours and the rest is thrown out.

Why the preservative is the whole point

Benzyl alcohol disrupts bacterial cell membranes, preventing contamination introduced by a needle from multiplying. "Bacteriostatic" means it inhibits reproduction rather than killing outright. That would be bactericidal.

That inhibition is what makes a multi-dose vial possible. Reconstituted peptide is a nutrient-rich solution sitting in your fridge, punctured repeatedly over weeks. Sterile water offers it no protection at all, which is why a vial reconstituted with sterile water is single-use and must be discarded within 24 hours.

For essentially every peptide in this library, bacteriostatic water is the correct answer.

The exceptions

Three compounds get preservative-free sterile water instead: oxytocin, NAD+ and KPV. For each, sources disagree, and Claritide takes the cautious side: sterile water, and 24 hours. Our own list says sterile water, dosing guides mix them with bacteriostatic water, and we found no study of any of the three in benzyl alcohol. Oxytocin's FDA labels do not settle it: Pitocin and a generic we read are ready-made solutions preserved with chlorobutanol, not benzyl alcohol. When you use sterile water, treat the vial as single-use: prepare the dose and discard the remainder within 24 hours.

hCG is not an exception. Its FDA labels mix it with a diluent preserved with benzyl alcohol. Novarel's label says to refrigerate the mixed vial and use it within 30 days. Pregnyl's says the mixed solution is stable for 60 days when refrigerated.

Normal saline is not the answer either. Plain bacteriostatic normal saline exists, but the sodium chloride is unnecessary for most peptides and can occasionally affect stability or pH. Plain bacteriostatic water is the standard.

Tap water, distilled water and any non-sterile water are not options at any point, for any compound. They cause infections, abscesses and sepsis.

The arithmetic

Two formulas cover every reconstitution you will ever do.

Concentration (mg/mL) = peptide amount (mg) ÷ water volume (mL)

Dose volume (mL) = desired dose (mg) ÷ concentration (mg/mL)

On a U-100 insulin syringe, 1 unit = 0.01 mL. So 10 units is 0.1 mL, 50 units is 0.5 mL, 100 units is the full barrel at 1 mL.

Worked: a 5 mg vial with 2 mL of bacteriostatic water gives 2.5 mg/mL. A 250 mcg dose is 0.25 mg, so 0.25 ÷ 2.5 = 0.1 mL, which is 10 units.

The volume you add does not change how much peptide you own. It only changes the concentration, and therefore how many syringe ticks a dose occupies. More water makes small doses easier to measure accurately but means larger injection volumes. Less water means smaller injections but demands more precision. One to two millilitres is the sweet spot for most peptides.

Handling

Wipe both stoppers with alcohol and let them dry before every puncture, even on a vial you just opened. Angle the needle so the water runs down the inside glass wall. Never spray it directly onto the powder, because the force can denature the peptide.

Swirl or roll the vial between your fingers until dissolved, usually one to three minutes. Never shake. Shaking causes foaming and mechanical stress that damages the molecular structure and costs you potency.

Inspect before use, every time. The solution should be completely clear. Cloudiness, floating particles, discoloration or an unusual odour means discard it, regardless of how recently you mixed it.

Label the vial with the date, the peptide name and the concentration, then refrigerate immediately.

Shelf life

An opened bacteriostatic water vial keeps for 28 days, room temperature or refrigerated. Reconstituted peptide keeps 28 days refrigerated at 2–8°C. Reconstituted with sterile water: 24 hours.

Never freeze reconstituted peptide. Ice crystals destroy the molecular structure. Lyophilized powder is the form that goes in the freezer: 1–2+ years at −20°C, or several months at 2–8°C in the fridge.

Store vials upright, so the solution is not in permanent contact with the rubber stopper.