Bacteriostatic Water: What Needle to Use and How to Draw It
Reconstitution basics
Some freeze-dried (lyophilised) products come as a powder sealed in a small glass vial. Reconstitution means adding a measured amount of the specified sterile liquid (diluent) to dissolve it. The steps here cover handling only, where your prescriber, pharmacist or product instructions require reconstitution. It doesn't advise whether any product should be used or injected.
Bacteriostatic water is sterile water with 0.9% benzyl alcohol as a preservative. Use it only when your instructions or a healthcare professional specify it. Don't use it where benzyl alcohol or preservatives are contraindicated, including for neonates or infants, or where a preservative-free diluent is required. Some products need preservative-free sterile water, sterile saline or a specified dilute acid instead.
The "what needle" question covers two jobs:
- Drawing the bacteriostatic water and adding it to the product vial, covered below.
- Withdrawing the finished solution later, only for a prescribed, approved product, with the syringe and needle specified for that route and volume.
The volume you add usually sets the concentration, but take the concentration only from your instructions, including any stated final volume. We don't advise on volumes or doses here.
Two ways to draw and add bacteriostatic water
1. A draw-up syringe (the convenient option)
Use a sterile syringe sized for the volume. A 10mL 18G draw syringe moves larger volumes quickly when your instructions allow that gauge. Use it for transfer only and keep punctures to a minimum. Ask your pharmacist if small vials or repeated access need a smaller draw needle or another device.
2. Standard insulin syringes (in a pinch)
For very small volumes, a fresh 1mL insulin syringe works. For 2 to 3mL, use a draw-up syringe where you can, because each insulin syringe adds a puncture and more handling. If your instructions allow insulin syringes, use each one once:
- 1mL transfer: one new 1mL insulin syringe.
- More than 1mL: one new 1mL insulin syringe per pass, discarded after each.
On a U-100 insulin syringe, 100 units = 1mL and each mark is 0.01mL. These are volume marks, not dose units.
The main reason for single use is contamination. An insulin syringe's needle is fixed, so if you refill it from the water vial after it's been in the product vial, you carry residue back into your water stock. A fresh syringe each pass closes that route. Clean stoppers and careful technique still matter, and reuse also blunts the needle.
Write the first-puncture date on the bacteriostatic water vial, store it as the label says, and discard it after the labelled in-use period, or sooner if you suspect contamination.
Step by step
- Wipe the stoppers on the water vial and the product vial, each with its own fresh alcohol wipe, and let them air-dry.
- Draw the specified volume: one pull with a draw-up syringe, or a new insulin syringe for every pass, including a partial last one. Discard each syringe after transferring.
- Pierce the product vial's stopper and let the water run slowly down the inside of the glass, not straight onto the powder. This cuts foaming.
- Remove the needle. Gently swirl or roll the vial unless your instructions say otherwise. Don't shake unless they allow it. Check the expected appearance and dissolving time in your instructions.
- Put every used needle and syringe straight into a sharps container.
Which gauge for which job
- Drawing and adding water: an 18G draw-up needle moves larger volumes fast when your instructions allow it. Use it for transfer only.
- Injecting, if prescribed: some subcutaneous products use short 4 to 6mm insulin needles, but the length, gauge, site and technique come from your instructions and healthcare professional. With detachable needles, it's common to draw with a thicker needle and switch to a fine one to inject. Fixed-needle insulin syringes can't be swapped.
Supplies you'll need
- Bacteriostatic water (10mL vial): the specified diluent for some products, not all.
- Draw-up syringe with sterile 18G draw needle: for larger transfers when your instructions allow 18G. Not for injecting or drawing doses. Also in a 5 pack, 10 pack or 100 box.
- 1mL insulin syringes: for very small diluent volumes, and for drawing doses of a prescribed product where syringe use is specified. Also in a 10 pack or 20 pack.
- 70% isopropyl alcohol wipes: for stoppers before every puncture.
- A sharps container from our sharps disposal range.
Common issues and what to do
- Foaming or bubbles: usually from adding water too fast or shaking. Small bubbles from normal drawing settle on their own.
- Tiny floating fragments (coring): bits of stopper shaved off by repeated punctures, poor technique, damaged needles or a needle too large for the job. Use fresh sterile equipment, keep punctures down and don't use the vial if particles appear.
- Cloudy solution: give it time and gentle swirling unless your instructions say otherwise. Don't heat it. If it doesn't end up matching the product description, don't inject it.
- Running short on syringes: if you regularly add 2 to 3mL, a draw-up syringe saves several insulin syringes per mix.
When to stop and call your prescriber
Stop injecting and contact your prescriber, doctor or local health service for:
- Signs of infection at a site: spreading redness, warmth, swelling, increasing pain or pus
- Fever, chills, or feeling generally unwell after injecting.
Don't inject, and contact your prescriber or pharmacist, if the solution is cloudy, discoloured or has particles. The same applies if you used the wrong diluent or volume, the concentration is uncertain, storage was breached or you suspect a dose error.
Signs of an allergic reaction: rash, hives, facial or throat swelling, or any difficulty breathing. This is an emergency - call 000 immediately.
Frequently asked questions
Can I use an insulin syringe to add bacteriostatic water?
Yes, for very small volumes. For 2 to 3mL, a draw syringe is better because several insulin syringes mean more punctures. Use a new sterile syringe for each pass, including a partial last one, and discard it straight after.
A vial storage case keeps vials upright and protected, but doesn't control temperature. Store and carry each vial as its label or pharmacist says, using an insulated or cold-chain method if needed.
What size needle is best for drawing bacteriostatic water?
An 18G draw-up needle is fast for larger volumes when your instructions allow it. A 1mL insulin syringe works for very small additions. Ask your pharmacist if small vials or repeated access need a different device.
Can I reuse a syringe to save needles?
No. Needles and syringes are single use. Refilling a fixed-needle syringe from the water vial after it's been in the product vial can contaminate your water stock, and reuse blunts the needle.
Should I shake the vial to dissolve the powder faster?
No, unless your instructions allow it. Add the water gently down the glass and swirl to keep foaming down.
Getting set up
You need the specified diluent, a clean way to draw it and safe disposal. Our reconstitution supplies range has bacteriostatic water, draw-up and insulin syringes, alcohol wipes and sharps containers in one place.
This article is general information about injection supplies and technique, not medical advice, and gives no dosing guidance. Our bacteriostatic water and supplies are for use with medicines prescribed and supplied by a registered health practitioner. Follow your prescriber's and pharmacist's instructions. We don't supply, or advise on, unapproved substances.
