Bacteriostatic Water (BAC water)

What it is

Bacteriostatic water, usually shortened to BAC water, is sterile water for injection with 0.9% benzyl alcohol added. The benzyl alcohol is a preservative. It does not sterilise anything, but it makes it much harder for bacteria to grow in the vial if a needle goes in more than once.

That is why it is the default liquid for mixing freeze-dried peptides. A peptide vial gets used over days or weeks, so you need a liquid that copes with repeated needle punctures. Whether you are mixing BPC-157, GLOW, HCG or most others on this site, BAC water is almost always the answer unless the vendor tells you otherwise.

It is not the same as plain sterile water for injection (no preservative, single use only) or saline (salt water). Mixing them up is a common beginner mistake, so it is worth knowing the difference before you order.

History

Bacteriostatic water has been a standard hospital and pharmacy product for decades, used to dilute or dissolve injectable medicines supplied in multi-dose vials. Using it for peptides is just borrowing a long-established medical supply for a new purpose.

How it works

Benzyl alcohol at 0.9% slows or stops the growth of many common bacteria (that is what "bacteriostatic" means: it holds bacteria back rather than killing them outright). If a few bacteria get in on a needle tip, the preservative limits how far they can multiply. It is a safety margin, not a licence for sloppy technique. You still wipe the stopper with an alcohol swab every single time and use a fresh sterile needle.

Dosage

• There is no dose of the water itself. The question is how much to add to a peptide vial, and that decides how big each dose is in units on your syringe.
• The principle: concentration = amount of peptide divided by volume of water. A 1 ml insulin syringe holds 100 units, so units = ml x 100. A bigger volume means a more dilute mix, so you draw more units for the same dose.
• Worked example: a 5 mg vial plus 2 ml of BAC water gives 2.5 mg per ml, which is 2,500 mcg per ml, or 25 mcg per unit. For a 250 mcg dose you draw 10 units. For 500 mcg, 20 units.
• Same 5 mg vial plus 1 ml gives 5,000 mcg per ml, or 50 mcg per unit. A 250 mcg dose is 5 units. Fewer units is harder to measure accurately, which is why many people prefer more water.
• A sensible approach is to choose a volume that makes your usual dose a round, easy-to-read number of units, then write the maths on the vial label so you do not have to redo it half asleep.
• The vial has to physically hold the water. Do not add more than the peptide vial can take. Always check the peptide vial size before planning.

How it is taken

• BAC water is not injected by itself. It is drawn into a sterile syringe, then injected into the sealed peptide vial to dissolve the powder.
• Wipe the stopper on both vials with a fresh alcohol swab and let it dry. Use a sterile syringe and needle for each step.
• It is not suitable for large-volume or intravenous use. The benzyl alcohol is only appropriate in small volumes. Never use it as an IV flush or infusion fluid.
• It should not be used for neonates or very young infants. Benzyl alcohol has been linked to a serious and sometimes fatal "gasping syndrome" in premature babies. If infants are in the household, store vials safely out of reach, and ask a pharmacist if you are unsure.

How to reconstitute

• Draw up the amount of BAC water you have decided on. Inject it slowly down the inside wall of the peptide vial rather than blasting it onto the powder.
• Let it run down and dissolve on its own. Gently roll or swirl the vial if needed. Do not shake: foaming can damage fragile peptides. Most dissolve within a minute or two. Some need a few minutes.
• Worked example again: 5 mg peptide + 2 ml BAC water = 2.5 mg/ml = 25 mcg per unit on a 1 ml (100-unit) syringe.
• Another: 10 mg peptide + 2 ml = 5 mg/ml = 50 mcg per unit. 10 mg + 4 ml = 2.5 mg/ml = 25 mcg per unit.
• Do the sum, then check it a second time. A decimal point error means a tenfold dosing error. If you are unsure, use a reconstitution calculator and confirm by hand.
• Some peptides do not dissolve well in plain BAC water and need a dilute acid instead. See the Acetic Acid Water page. IGF-1 LR3 is the usual example.

How it should arrive

A small glass vial with a rubber stopper and an intact crimped metal cap (often with a flip-off plastic top). The cap should be sealed and undamaged. The label should state "bacteriostatic water", "0.9% benzyl alcohol" and have a batch number and expiry date. This seller stocks 3 ml and 10 ml vials.

How it should look once reconstituted

Completely clear and colourless, with no particles, fibres, floating specks or cloudiness. If it is cloudy, has anything floating in it, or the cap was loose or already broken, do not use it. Throw it away.

What to expect, and when

• Unopened: good until the printed expiry date if stored properly.
• Once the stopper has been punctured, the standard rule for multi-dose vials is to discard after 28 days, even if there is liquid left. Write the date you first opened it on the vial.
• Peptide mixed with it follows its own limit, which is usually shorter or similar, and it should live in the fridge.
• A 10 ml vial is cost-effective, but if you only mix a couple of vials a month you may not finish it within 28 days. A 3 ml vial wastes less in that case.
• The 28-day rule is a convention from pharmacy practice, not a hard biological cliff. Going longer raises the infection risk, and the cost of new water is tiny compared with the cost of an abscess.

Side effects

• Stinging or burning on injection, usually mild. It can come from the benzyl alcohol or from the peptide itself.
• Redness, itching or a small rash at the injection site, which could be a sensitivity to benzyl alcohol. This is uncommon but real.
• If you notice stinging with every injection, and not just with one peptide, try a slower injection, or ask a pharmacist about preservative-free options.
• Rare allergic reactions (widespread rash, swelling of the face or lips, difficulty breathing) need emergency help immediately.

Risks

• Contamination is the main risk, not the water itself. A poorly cleaned stopper, a reused needle or a dirty surface can put bacteria in the vial. The preservative reduces the risk but does not remove it.
• It is not for neonates or premature babies (benzyl alcohol toxicity). It is not for intravenous use or large volumes.
• Do not substitute plain sterile water if the vial will be used more than once: with no preservative, bacteria can grow quickly.
• Do not substitute saline for reconstituting unless a specific protocol says so. Some peptides behave differently in salt solutions.
• Do not use distilled water from the shop, tap water, or cosmetic or steam-iron water. These are not sterile and are dangerous to inject.
• Buy from a source that supplies a genuine product with a batch number. A fake or non-sterile vial is a serious risk.

Potential gains

• Lets one peptide vial be used safely over several weeks without needing to use it all in one go.
• Cheap, easy to find, and works with the great majority of research peptides.
• Available in vial sizes that suit both occasional and frequent mixers.
• Gives you flexibility to choose the volume so the dose maths works out to numbers that are simple to read on a syringe.

Other useful information

Know the three liquids. Bacteriostatic water: sterile water plus 0.9% benzyl alcohol, multi-dose. Sterile water for injection: sterile water with no preservative, single use only, discard the leftover. Saline (0.9% sodium chloride): salt water, a different product with different uses, not a drop-in swap. Acetic acid water is a fourth option for a few peptides that will not dissolve in plain water. For most people, BAC water is the one to buy. Put a sticker on every vial with the date first opened, the volume of water added and the units per dose.