The quick comparison

Water What it is Preservative? Best for
Bacteriostatic water Sterile water with 0.9% benzyl alcohol Yes Multi-dose vials when the product instructions specify it
Sterile water for injection Sterile water, nothing added No Single use - mix and use immediately
Saline (0.9% sodium chloride) Sterile salt solution Plain: no Mostly IV dilution; not the usual peptide diluent
A vial of bacteriostatic water with an insulin syringe, used only when specified by product or pharmacy instructions
A vial of bacteriostatic water with an insulin syringe. Use bacteriostatic water only when it is specified by approved product information, your prescriber, or your pharmacist.

Bacteriostatic water - preserved sterile water

Bacteriostatic water is sterile water with 0.9% benzyl alcohol added as a preservative. The preservative helps inhibit bacterial growth after puncture. Follow the diluent label, approved product information, and your prescriber's or pharmacist's instructions for discard timing; reconstituted product storage and shelf life vary by medication. Bacteriostatic water is commonly specified for some multi-dose use, but it is not a default substitute for product-specific directions.

Sterile water - single use only

Sterile water for injection is just that: sterile water with nothing added. With no preservative, sterile water is generally treated as single-use once opened, and any remaining diluent should be discarded. After mixing, follow the product-specific storage and discard instructions; if none are supplied, do not store or reuse it. Benzyl alcohol is not suitable for newborns, and a small number of people are sensitive to it. In those cases, approved product information, the prescriber, or the pharmacist may specify sterile water or another suitable diluent; the vial should then generally be treated as single-use unless instructed otherwise.

Saline - not the usual choice

Saline is 0.9% sodium chloride - a sterile salt solution used widely for intravenous fluids and dilution. Plain saline has no preservative, so like sterile water it is single-use once opened. A preserved version (bacteriostatic saline) exists, but diluent choice is product-specific. Use only the diluent directed by approved product information, your prescriber, or your pharmacist.

Bottom line

Do not choose a diluent by default. For a multi-dose peptide vial, use bacteriostatic water only when approved product information, your prescriber, or your pharmacist specifies it. Choose sterile water, saline, or another diluent only when those same instructions specify it. Never substitute any non-sterile water.

Supplies

  • 10mL bacteriostatic water vial - preserved sterile water used only when specified by approved product information, your prescriber, or your pharmacist.
  • 10mL syringe with an 18G draw needle - can transfer diluent efficiently when that syringe size and gauge are appropriate. Use the gauge recommended for the vial, stopper, and technique, and avoid repeated large-gauge punctures that can damage the stopper.
  • 0.5mL insulin syringes (31G, 6mm) - for drawing each dose only when this syringe type matches the prescribed route, volume, and product instructions. Use a new sterile syringe and needle for each draw/injection; do not reuse an insulin syringe or use one fixed-needle syringe across multiple vials.
  • Alcohol wipes (200-pack) - swab every stopper.

Browse the full injection supplies range.

Frequently asked questions

Can I use sterile water instead of bacteriostatic water?

You can only if approved product information, your prescriber, or your pharmacist specifies sterile water. Because sterile water has no preservative, it is generally treated as single-use once opened or mixed unless the supplied instructions say otherwise. For a multi-dose vial, use bacteriostatic water only when it is specified.

Tip: a vial storage case keeps vials upright, cushioned and organised. It is for physical protection and organisation only; follow the product's temperature requirements separately.

Is saline OK for reconstituting peptides?

Use saline only if approved product information, your prescriber, or your pharmacist specifies it. Plain saline has no preservative and is generally treated as single-use once opened unless the supplied instructions say otherwise.

Why can't I just use tap or distilled water?

Because they are not sterile. Injecting a solution mixed with non-sterile water risks introducing bacteria. Always use a purpose-made sterile diluent.

Who should not use bacteriostatic water?

It is not suitable for newborns, and a small number of people are sensitive to benzyl alcohol. In those cases, approved product information, your prescriber, or your pharmacist may specify sterile water or another suitable diluent; the vial should then generally be treated as single-use unless instructed otherwise.

This guide compares injection supplies and is not medical advice. Follow approved product information and your prescriber's or pharmacist's instructions for your specific medication.