Bac Water 3 mL: What It Is, What It's Used For, and How to Store It

Bac water 3 mL is a 3-milliliter vial of bacteriostatic water — sterile water that contains 0.9% benzyl alcohol — used to dissolve, or reconstitute, freeze-dried peptides and other lab powders. The benzyl alcohol acts as a preservative, so the same vial can be punctured with a syringe more than once. The 3 mL size is the smallest standard vial, which makes it a practical choice when only a small amount of diluent is needed.

What Is Bac Water 3 mL Made Of?

Bacteriostatic water for injection, usually shortened to bac water, is sterile water with 0.9% benzyl alcohol added by volume. The alcohol does not sterilize the water; it inhibits bacterial growth so a multi-dose vial stays usable for weeks instead of hours.

Bac water 3 mL is not the same as plain sterile water, which has no preservative and is intended for single use. It is also not the same as normal saline, which contains 0.9% sodium chloride instead of benzyl alcohol.

• Sterile water base with no sodium chloride and no buffer
• 0.9% benzyl alcohol as the bacteriostatic preservative
• Multi-dose vial designed for repeat needle punctures
• Unbuffered, typically around pH 5.0 to 7.0

Why the 3 mL Size Is Popular — and When to Size Up

Small vials cut waste. If a single 5 mg peptide needs 1 to 2 mL of diluent, a bacteriostatic water 10ml vial leaves most of the liquid unused, and any punctured vial still expires about 28 days later.

Larger volumes make sense for labs that reconstitute many compounds from one workbench. Neither size is stronger than the other, because concentration depends on how much powder you add and how much liquid you draw out.

Vial Size	Typical Fit	Practical Note
3 mL	One or two small peptide vials	Lowest upfront cost, least wasted diluent
10 mL	Multi-compound or bulk workflows	Fewer reorders, same 28-day in-use window
30 mL	High-volume or institutional use	Usually comes through medical supply channels

How to Reconstitute a Powder With 3 mL of Bac Water

If you are learning how to mix bac water with peptides, the process is the same whether you use a 3 mL vial or a larger one. Clean technique matters more than vial size.

1. Wipe both stoppers with an alcohol swab and let them air-dry.
2. Draw air into the syringe equal to the volume of bac water you plan to add, then inject that air into the bac water vial to equalize pressure.
3. Withdraw the bac water and insert the needle into the powder vial at an angle so the stream runs down the glass wall instead of hitting the powder directly.
4. Swirl the vial gently. Do not shake, because shaking can damage fragile peptides.
5. Label the vial with the date and concentration, then refrigerate it.

Run the numbers with a bac water calculator before you draw anything out. With only 3 mL in the vial, a small measuring error changes the final concentration more than it would in a larger volume.

Powder Mass	Concentration With 3 mL	Volume Equal to 250 mcg	Units on a U-100 Syringe
1 mg	0.33 mg/mL (333 mcg/mL)	0.75 mL	75 units
2 mg	0.67 mg/mL (667 mcg/mL)	0.38 mL	38 units
5 mg	1.67 mg/mL (1,667 mcg/mL)	0.15 mL	15 units
10 mg	3.33 mg/mL (3,333 mcg/mL)	0.08 mL	8 units

Those figures are arithmetic, not medical guidance. Lab math tells you what is in the syringe, not what is safe or appropriate for any person.

Storage and Shelf Life After the First Puncture

A common question is how long is bac water good for once opened, and the standard answer for a multi-dose vial is about 28 days when it is refrigerated and handled with clean technique. Refrigeration slows bacterial growth, but it does not reset that clock.

Write the puncture date on the label and discard the vial after the manufacturer's in-use window. Throw it out sooner if the solution looks cloudy, contains particles, or the stopper is damaged.

• Keep unopened vials at controlled room temperature, away from light.
• Refrigerate after the first puncture; do not freeze.
• Never reuse a syringe to draw from a multi-dose vial.
• Keep vials out of direct sunlight and away from heat sources.

Where to Buy Bac Water 3 mL in the United States

When people ask bacteriostatic water where to buy, the answer usually splits into two channels. The pharmacy channel supplies bacteriostatic water for injection as a prescription-labeled product in most settings. Large chains such as Walgreens, CVS, and Walmart sometimes stock it behind the counter, but many locations will not sell it without a prescription or a documented medical need. Availability varies by store and by state, so call ahead and ask the pharmacist.

The research channel is different. Many online suppliers sell 3 mL and 30 mL vials labeled for research use only, not for human use. Those products are not FDA-approved for human injection, no matter how they are marketed.

• Look for a USP-grade product with a lot number and expiration date.
• Check that the vial is sealed and the stopper is intact.
• Treat unusually low prices as a warning sign rather than a bargain.

Safety and Legal Points to Keep in Mind

Bacteriostatic water includes benzyl alcohol, which makes it unsuitable for intravenous, intrathecal, epidural, and ophthalmic use. It also should not be used to dilute medications intended for newborns.

Bacteriostatic water sold for research use is not FDA-approved for human injection. Anyone considering injectable peptides should talk with a licensed healthcare professional about legality, sterility, and individual risk before proceeding.

The most common mistakes with a 3 mL vial are easy to avoid:

• Using bac water to dilute a drug labeled for single use only
• Shaking the vial to speed up dissolution
• Keeping a punctured vial well past 28 days
• Assuming a research-grade vial is the same as a pharmacy-grade product

Used correctly, a 3 mL vial of bac water is a low-cost, convenient diluent for small peptide batches. Treated casually, it becomes a contamination and dosing-error risk that no amount of convenience justifies.

COMMON QUESTIONS

Frequently Asked Questions

What is bac water 3 mL used for?

Bac water 3 mL is used to dissolve freeze-dried peptide powders and other lab compounds so they can be measured and handled as a liquid. The benzyl alcohol preservative allows the same vial to be punctured multiple times, which suits small, repeated reconstitutions. It is a diluent only, not an active product on its own.

How long does bac water 3 mL last after opening?

Most manufacturers treat a punctured multi-dose vial of bacteriostatic water as usable for about 28 days when refrigerated. Discard it sooner if the solution becomes cloudy, shows particles, or the stopper is damaged. Never use a vial past its printed expiration date, even if it was never opened.

Can I buy bac water 3 mL at Walgreens or CVS?

Bacteriostatic water for injection is typically a pharmacy item, and many locations keep it behind the counter, so availability varies and a prescription may be required. Some pharmacies stock 30 mL vials instead of 3 mL. Online 3 mL vials are usually sold for research use only and are not FDA-approved for human injection.