Last updated 18 September 2026 · SARMs Store editorial team. Products on this site are supplied strictly for laboratory research and are not for human consumption. This guide summarises published research; it is not medical advice and contains no instructions for use. 18+ only.
Bacteriostatic water at a glance
| What it is | Sterile water containing 0.9% benzyl alcohol as a preservative |
|---|---|
| Purpose | Laboratory reconstitution of lyophilised peptides where a multi-use vial is needed |
| Differs from | Sterile water for injection (no preservative, single use) and normal saline (0.9% sodium chloride) |
| Convention | Once a vial is punctured, laboratories discard after 28 days |
| Format | 10ml vial |
| Storage | Room temperature, away from light; do not freeze |
| UK status 2026 | Supplied as a laboratory reagent for research use |
Bacteriostatic water UK: what to know before you buy
Bacteriostatic water, often shortened to bac water or BAC water, is the diluent most peptide buyers in the UK order alongside their vials. It is sterile water with 0.9% benzyl alcohol added, which is what lets a vial be entered more than once without the contents spoiling. That single difference is why it is sold next to almost every lyophilised peptide, and why it is the most searched laboratory accessory in the peptide category.
Our Origin Peptides Bacteriostatic Water 10ml is a sealed, batch-numbered multi-dose vial with a rubber stopper and flip-off cap, dispatched from our UK warehouse with the rest of the Origin Peptides range. It costs £5.99, and it counts towards the multibuy discount when ordered with peptides.
Bacteriostatic water vs sterile water vs saline
| Bacteriostatic water | Sterile water | Normal saline | |
|---|---|---|---|
| What it is | Sterile water plus 0.9% benzyl alcohol | Sterile water, nothing added | 0.9% sodium chloride in water |
| Multi-use | Yes, 28 days after first puncture by convention | No, single use once opened | Depends on whether it is preserved |
| Typical use in peptide work | The default diluent for lyophilised peptides | Peptides or methods sensitive to benzyl alcohol | Methods that need an isotonic solution |
| Storage | Room temperature, out of sunlight | Room temperature, sealed | Room temperature, sealed |
Bac water, BAC water and the other names
You will see the same product listed as bacteriostatic water, bac water, BAC water, bacteriostatic water for injection (the pharmacopoeial name) and BW. Some listings say "0.9% benzyl alcohol", others "9mg/ml benzyl alcohol": they are the same concentration. A product described simply as "sterile water" is a different thing and has no preservative.
Which peptides it is used with
Bacteriostatic water is the standard diluent across the range: BPC-157, TB-500, GHK-Cu, CJC-1295 with Ipamorelin, Tesamorelin and the blends such as Wolverine and GLOW. A few compounds and some cell culture methods avoid benzyl alcohol, and the data sheet or literature for each compound is the guide there.
What a good bacteriostatic water listing shows
- The benzyl alcohol concentration, 0.9%.
- The volume per vial, usually 10ml or 30ml.
- A batch number and an expiry date on the vial.
- Sterility and endotoxin testing on the certificate.
- A proper sealed vial with a rubber stopper, not a dropper bottle.
What bacteriostatic water is
Bacteriostatic water is water that has been sterilised and then had 0.9% benzyl alcohol added. Benzyl alcohol does not kill microorganisms outright; it stops them multiplying, which is what bacteriostatic means. That property allows a vial to be entered more than once in the laboratory without the contents becoming a culture. It is the standard diluent for lyophilised research peptides for that reason.
How it differs from the alternatives
Sterile water for injection is the same water without the preservative. It is intended for single use: once opened, anything that gets in can grow. Normal saline is 0.9% sodium chloride, matched to the salt content of body fluids, and may or may not carry a preservative. Some peptides are sensitive to benzyl alcohol or to salt, and the manufacturer's data sheet, or the research literature for that peptide, should decide which diluent a laboratory uses. This guide does not give reconstitution instructions; those belong to the laboratory protocol for each compound.
The 28-day convention
Pharmacopoeial guidance treats a multi-dose vial as usable for 28 days after first puncture, provided it is stored as labelled and each entry is made with a fresh sterile needle. After that the preservative can no longer be relied on. Laboratories date the vial on first use.
Storage and handling
Store at room temperature, away from light. Do not freeze; freezing can compromise the seal and the preservative. Discard if cloudy, discoloured or past the labelled expiry. Benzyl alcohol is not suitable for every application; it is toxic to neonates and is avoided in some cell culture work, which is why sterile water without preservative is also stocked.
What to check before buying
A pharmacopoeial grade statement (USP or BP), the benzyl alcohol concentration, sterility and endotoxin testing on the certificate, an intact seal and a clear expiry date.
Frequently asked questions
Is bacteriostatic water the same as sterile water?
No. Bacteriostatic water contains 0.9% benzyl alcohol as a preservative; sterile water has none and is single use.
How long does an opened vial last?
The laboratory convention is 28 days from first puncture when stored as labelled.
Can it be frozen?
No. Freezing risks the seal and the preservative.
Why do some protocols avoid benzyl alcohol?
Some peptides and some cell culture applications are sensitive to it; sterile water without preservative is used instead.
Can you buy bacteriostatic water in the UK?
Yes. Our 10ml vial is supplied as a laboratory reagent and dispatched from our UK warehouse by tracked delivery.
What is the difference between bac water and bacteriostatic water?
None. Bac water and BAC water are short names for bacteriostatic water.
Why is bacteriostatic water sold with peptides?
Peptides are supplied as a freeze-dried powder, and bacteriostatic water is the standard laboratory diluent for them because the benzyl alcohol keeps a vial usable for repeated entry.
Is 9mg/ml benzyl alcohol the same as 0.9%?
Yes. 9 milligrams per millilitre is 0.9%.
Key references
United States Pharmacopeia. Bacteriostatic Water for Injection monograph. Centers for Disease Control and Prevention. Questions about multi-dose vials (28-day beyond-use date guidance). British Pharmacopoeia. Water for Injections monograph.
Related guides
- BPC-157 research guide
- TB-500 research guide
- SARMs vs peptides: what the research compares
- How to read a certificate of analysis
Research products: Origin Peptides bacteriostatic water 10ml · Full Origin Peptides range · Lab Testing