Bacteriostatic water

Bacteriostatic water is sterile water with a small amount of preservative added. The standard product, Bacteriostatic Water for Injection, contains 0.9% benzyl alcohol (9 mg per mL). “Bacteriostatic” means the preservative stops bacteria from multiplying; it does not kill everything, and it does not make a contaminated vial safe.

It is used to dissolve or dilute medicines and other powders, including freeze-dried peptides, in vials that will be used more than once. The preservative is the whole point: each time a needle goes through the stopper there is a chance of introducing bacteria, and benzyl alcohol keeps them from growing between uses.

The FDA-approved product label gives the formal definition. The Hospira label on DailyMed describes it as a sterile, nonpyrogenic preparation of Water for Injection containing 0.9% (9 mg/mL) or 1.1% (11 mg/mL) benzyl alcohol, supplied in a multiple-dose container from which repeated withdrawals may be made. It gives the pH as 5.7, within a range of 4.5 to 7.0. “Nonpyrogenic” means free of the fever-causing bacterial residues discussed further down. “Bac water” is simply the everyday short name for the same product.

The label is narrow about this. It says the product is indicated only for diluting or dissolving drugs for intravenous, intramuscular or subcutaneous injection, according to the instructions of the manufacturer of the drug being given. It is a diluent: a liquid for making up something else, not a treatment in its own right.

Several prescription medicines are sold as freeze-dried powders with bacteriostatic water in the pack. Two examples from their FDA labels:

• EGRIFTA WR, a brand of tesamorelin, comes with a 30 mL multiple-dose bottle of Bacteriostatic Water for Injection. Each 11.6 mg vial is mixed with 1.3 mL, giving 8 mg/mL (EGRIFTA WR label).
• Novarel, a chorionic gonadotropin (hCG) product, comes with a 10 mL vial of Bacteriostatic Water for Injection containing 0.9% benzyl alcohol (Novarel label).

Bac water for peptides is the same idea applied to research material. Research peptides such as BPC-157 are usually sold as a dry powder in a sealed vial, and bacteriostatic water is the liquid most suppliers’ instructions name for dissolving them. If research peptides are new to you, what research peptides are explains the category and why it sits outside the approved-medicine system.

The two look identical but behave differently:

• Bacteriostatic water contains benzyl alcohol, comes in multi-dose vials and is intended for repeated use over a limited period.
• Sterile water for injection contains no preservative. It is sterile until opened, and is intended for single use: once the seal is broken, there is nothing to stop bacterial growth.

That difference matters for storage. A peptide mixed with sterile water should be treated as single-use; one mixed with bacteriostatic water can be kept in the fridge and used over a longer period, subject to the stability of the peptide itself. Our guide to storing peptides covers both.

The Serostim label, for a somatropin (growth hormone) product, shows the trade-off in one product. Made up with bacteriostatic water, the 4 mg vial may be kept in the fridge at 2–8 °C for up to 14 days. Made up with Sterile Water for Injection instead, the solution is to be used immediately, one dose per vial, with any remainder thrown away. It says to use sterile water instead for anyone with benzyl alcohol hypersensitivity, and in pregnancy or breastfeeding.

A few peptides dissolve poorly in water and are reconstituted with other solvents, such as dilute acetic acid, in laboratory settings. Where that applies, the individual peptide page or the supplier’s instructions should say so.

Not necessarily. “Reconstitution solution” or “diluent” just means whatever liquid a product is made up with, and that varies. Some kits supply ordinary 0.9% bacteriostatic water; others supply their own liquid with a different preservative level. The Omnitrope label, for example, pairs its somatropin vials with a 1.14 mL diluent of Bacteriostatic Water for Injection containing 1.5% benzyl alcohol, stronger than the usual 0.9%. Other products use plain sterile water.

For an approved medicine, the rule is to use the diluent the label names; the EGRIFTA WR label, for one, says to use only the diluent provided. For a research peptide there is no approved label, so the supplier’s instructions are all there is. A supplier that sells a liquid called “reconstitution solution” should say what is in it, in the same detail as a bacteriostatic water label: water, preservative and concentration.

Saline is water with 0.9% sodium chloride, the same salt concentration as body fluids. It also comes in a bacteriostatic version, containing benzyl alcohol as a preservative. Saline is used as a diluent for some products, but salt can affect how some peptides dissolve and how stable they are in solution. Most research peptide suppliers and instructions refer to bacteriostatic water rather than saline; where a peptide needs something different, it should say so.

Hospira bacteriostatic water is the product most people mean when they search for a brand. Hospira has been a subsidiary of Pfizer since Pfizer completed its acquisition in September 2015, which is why the same vial is described as Hospira, Pfizer or Pfizer Hospira bacteriostatic water. It is an FDA-approved product, marketed under application NDA 018802 (Drugs@FDA).

The current Hospira bacteriostatic water for injection label on DailyMed states:

• Contents: Water for Injection with 0.9% (9 mg/mL) or 1.1% (11 mg/mL) benzyl alcohol, depending on the presentation.
• Sizes listed: a 30 mL multiple-dose plastic fliptop vial at 9 mg/mL, and a 20 mL fill in a 30 mL glass fliptop vial at 11 mg/mL, each sold in trays of 25.
• Storage: 20 to 25 °C (68 to 77 °F), controlled room temperature.
• Status: marked “Rx only” and “For drug diluent use only”, with a boxed warning: not for use in neonates.
• Handling: use aseptic technique for every entry into the vial; do not use unless the solution is clear and the seal intact.

Several US distributors repackage the Hospira product under their own names, with DailyMed labels that repeat the Hospira text.

The 30 mL vial is the size on the current Hospira label and the one bundled with EGRIFTA WR. The 10 mL size is the one packed with Novarel. The 10 mL, 3 mL and other small vials that people search for are sold by other makers and resellers; check their labels the same way as any other vial.

Size affects waste more than price. Once the stopper is first punctured, the in-use clock starts (next sections), and it runs the same for a 10 mL vial as for a 30 mL one. The worked examples further down use 1 to 5 mL per peptide vial, so most of a 30 mL vial is thrown away unless many vials are made up within that period. A small vial costs more per millilitre but wastes less, and each stopper takes fewer needle entries.

Unopened vials are normally stored at controlled room temperature, away from light, until the printed expiry date; check the label, as storage directions can differ between manufacturers. Once the stopper has been punctured, the vial has a limited in-use life (below). Keep the stopper clean, and do not use a vial that has been left open, has changed colour or contains particles.

The water itself does not. The Hospira label directs storage at 20 to 25 °C, and the EGRIFTA WR pack instructions say to keep the bacteriostatic water bottle in the injection box at room temperature, including after it has been opened. Neither label calls for refrigerating the water.

A peptide once mixed with bacteriostatic water is a different question, and the answer depends on the peptide. Approved products disagree with each other. The Novarel label says to refrigerate the reconstituted product at 2–8 °C and use it within 30 days. The Serostim label allows 2–8 °C for up to 14 days. The EGRIFTA WR label says the opposite for tesamorelin: keep the mixed vial at room temperature, do not freeze or refrigerate it, and discard it 7 days after mixing.

Research peptides have no approved label, so there is no official answer for them. The Hospira label itself says not to store reconstituted solutions unless the manufacturer of the dissolved drug directs it. Most research peptide guidance defaults to the fridge for mixed vials, as our peptide storage guide explains.

For multi-dose vials of injectable products, a common pharmacy standard is to discard the vial 28 days after it is first punctured, unless the manufacturer states a different period. Unopened vials keep until the expiry date printed on them, stored as the label says (usually at controlled room temperature).

That 28-day figure comes from the US Pharmacopeia’s chapter on sterile compounding, as summarised by the CDC’s injection safety guidance: once a multi-dose vial is opened or needle-punctured, it should be dated and discarded within 28 days unless the manufacturer states another date, and never used past the manufacturer’s own expiry date. The EGRIFTA WR instructions apply the same period to the bacteriostatic water in their kit: discard any left in the bottle 28 days after first use, and write the date of first use on the box.

So bac water does go bad: unopened, it lasts until the printed expiry date; opened, the usual limit is 28 days, or sooner if it becomes cloudy, discoloured or contains particles.

Keep in mind that there are two separate clocks once you have made up a peptide: how long the water stays usable, and how long the peptide stays intact in solution. The shorter of the two applies.

Adding water does not change how much peptide is in the vial. It only changes how concentrated the solution is. A worked example:

• A 5 mg vial with 2 mL of water gives 2.5 mg per mL, which is 2,500 mcg per mL.
• A U-100 insulin syringe is marked in units, with 100 units per mL. So 1 unit is 0.01 mL.
• At 2,500 mcg per mL, each unit holds 25 mcg, and 10 units (0.1 mL) holds 250 mcg.
• Add 1 mL instead of 2 and the solution is twice as strong: each unit then holds 50 mcg.

The peptide calculator does this arithmetic for any vial size and water volume. One caution it cannot fix: the calculation assumes the vial contains exactly what the label says. If a vial is under-filled, every figure is off by the same proportion. That is why quantity testing matters; see how to read a COA.

“How much bac water for 10mg retatrutide” is one of the most searched questions about bacteriostatic water. There is no single correct volume. Retatrutide is an investigational drug with no approved label, so no official reconstitution volume exists for it. Any volume gives the same total amount of drug in the vial; the water only decides how much liquid each milligram sits in. The figures below are arithmetic, not a recommendation of a volume or a dose.

The formula is: concentration (mg per mL) = milligrams in the vial ÷ millilitres of water. On a U-100 syringe, 1 unit is 0.01 mL, so milligrams per unit = concentration ÷ 100.

The same table answers the other vial-size searches, because the arithmetic does not depend on which peptide is in the vial. A 10 mg or 30 mg vial of tirzepatide, a 5 mg vial of semaglutide or BPC-157, and a 50 mg vial of GHK-Cu all follow the rows above. Two practical limits apply: the vial has to physically hold the water added, and very small volumes of a strong solution are hard to measure accurately on a syringe.

The retatrutide calculator works this through for any vial size and water volume, and the tirzepatide calculator does the same for tirzepatide. None of this is a recommendation. For approved medicines, the only dose is the one on the prescription and label; for unapproved compounds like retatrutide, no dose has been approved at all.

Prescription kits describe the same basic steps. The Novarel instructions start by removing the flip caps and wiping both vial tops with an alcohol pad. The EGRIFTA WR instructions add checking the expiry date on the medicine and the water, say not to shake the mixed vial, and say to use the solution only if it is clear, colourless and free of particles. The Hospira label adds aseptic technique for every entry into the vial, and notes that some drugs are incompatible with benzyl alcohol, one reason a label sometimes names a different diluent.

A research peptide solution that stays cloudy or has visible particles is a warning sign about the peptide or the water. Independent third-party testing is the only way to know what the powder actually is.

No, not to the standard the product is defined by. Home-made bacteriostatic water would miss that standard at three points.

Sterile and nonpyrogenic water. The label specifies Water for Injection that is both sterile and nonpyrogenic. Pyrogens are mainly bacterial endotoxins, which come from the outer membrane of Gram-negative bacteria. The FDA’s inspection guide on endotoxins notes that they are not removed by sterilising filters, that depyrogenating glassware takes dry heat of the order of 250 °C for 45 minutes, and that the two accepted ways of making Water for Injection are distillation and reverse osmosis. Boiling water kills many bacteria but does none of this.

An exact preservative dose. The product contains 9 mg of benzyl alcohol per mL (11 mg in the 1.1% version). That figure is set by the approved formulation and checked in manufacture; it cannot be measured reliably at a kitchen table.

Sterile filling and testing. A home mixture, including benzyl alcohol added to a sterile water vial, cannot be tested for sterility or endotoxins without laboratory equipment.

• Not for newborns. Benzyl alcohol has been linked to a serious toxic reaction in premature infants, so products containing it carry a warning against use in neonates.
• A diluent, not a product in itself. Bacteriostatic water is intended for dissolving or diluting other products, not for injection on its own: water with nothing dissolved in it is hypotonic.
• Check the seal and the expiry date, and do not use a vial that is cloudy or has particles in it.
• Buy from a source that states what it is. The label should state the benzyl alcohol content, the volume, a batch number and an expiry date.

On newborns, the Hospira label says only preservative-free Sterile Water for Injection should be used when preparing medicines for them. The Omnitrope label describes the “gasping syndrome” behind the warning (central nervous system depression, metabolic acidosis and gasping breathing), associated with benzyl alcohol dosages above 99 mg/kg/day in neonates and low-birth-weight neonates. The Novarel label notes it has been reported as fatal in premature infants.

The Hospira label also says benzyl alcohol preparations should not be used for fluid replacement or in epidural or spinal anaesthesia, and that the water given intravenously without a dissolved substance may cause haemolysis. Reactions it lists from the solution, the added drug or the technique include fever, abscess, infection or tissue necrosis at the injection site, and phlebitis. The Serostim label adds benzyl alcohol hypersensitivity as a reason to use sterile water instead.

Bacteriostatic water is a pharmaceutical product in its own right. How it is sold differs between countries: in some it is available from pharmacies, in others mainly through medical suppliers or online. When you buy it, check that the label names the manufacturer and states the benzyl alcohol content, volume, batch number and expiry date; that the flip-off cap and seal are intact; and that the liquid is clear. Unlabelled vials, or vials relabelled by a reseller with no manufacturer named, give you no way to know what you have.

Vials come in several sizes, commonly 10 mL or 30 mL. A larger vial is only better value if you will use it within its in-use period once opened; otherwise the unused water is wasted. Many peptide suppliers sell bacteriostatic water alongside their catalogue. The price is rarely what separates suppliers; delivery, testing and service usually matter more. Compare suppliers on those in the supplier directory or the best-rated ranking.

Searches for bacteriostatic water near me, at CVS, Walgreens, Boots, Chemist Warehouse or Amazon all come down to the same question: who can supply it where you live. In the US, the approved Hospira product is labelled “Rx only”, a prescription-only medicine, so pharmacies generally supply it against a prescription rather than off the shelf. When a prescription medicine comes with its own diluent, as EGRIFTA WR and Novarel do, the pharmacy supplies the water in the same pack. Rules for the UK, Australia and elsewhere are set by each country’s medicines regulator; ask a pharmacist rather than relying on a retailer’s listing.

Outside pharmacies, bac water is sold by medical supply companies, online marketplaces and many peptide suppliers. Not all of it is the same kind of product. DailyMed lists bacteriostatic water from at least one maker, Fujian Genohope Biotech, under the marketing category “unapproved drug other”, while the Hospira product and its repackagers are listed under the approved NDA. A vial’s label and its DailyMed or national registration tell you which you are looking at.

What makes the “best bac water for peptides” is therefore not a brand name but a checkable label: a named manufacturer, 0.9% benzyl alcohol stated, a batch number, an expiry date and an intact seal. The warning signs that apply to peptide sellers apply here too; see how to spot a fake peptide supplier. Peptide prices explained covers how add-ons like water change an order’s real cost, and peptide legal status in the US covers the peptides themselves.