BAC Water: Bacteriostatic Water Research Guide (2026)
Last updated
Introduction (research-only scope)
BAC water, bacteriostatic water, is not a research compound at all: it is sterile water containing about 0.9 percent benzyl alcohol as a preservative, used to reconstitute lyophilised material. It is the most-purchased item alongside peptides and the one most often bought without a second thought, which is exactly why it deserves a page.
Research use only. The material described here is a laboratory reagent for in-vitro research by qualified professionals. It is not a medicine, supplement, cosmetic ingredient or veterinary product, is not for human or animal use, and nothing on this page is medical advice or a claim of effect in any person.
What BAC Water is
BAC water is water for injection with benzyl alcohol added (water CAS 7732-18-5, benzyl alcohol CAS 100-51-6). There is no molecular mass to quote because it is a solvent, not a solute. Peptra Labs supplies it in 10 ml vials, intended as a laboratory diluent for reconstituting research reagents.
What benzyl alcohol does
Bacteriostatic, not sterilising
Benzyl alcohol inhibits bacterial growth in the vial after the stopper has been pierced; it does not sterilise contaminated material and does not make an unsterile procedure safe. That distinction is the whole point of the word “bacteriostatic”.
Why it matters which diluent you choose
Plain sterile water has no preservative, so a vial reconstituted with it is effectively single-use; bacteriostatic water is what allows repeated withdrawals over a defined period in laboratory practice.
What the literature says about preservatives and peptide stability
Preservatives are not inert with respect to proteins. A 2025 study in the European Journal of Pharmaceutics and Biopharmaceutics examined how antimicrobial preservatives affect protein folding stability and subvisible particle formation, which is the relevant literature when a peptide behaves unexpectedly after reconstitution. If a study design is sensitive to aggregation, the choice between preserved and unpreserved diluent is a variable to control, not a detail.
How to judge the quality of BAC Water
Two tests answer two different questions: mass spectrometry confirms identity (expected molecular mass not applicable: a solvent, not a defined solute), HPLC quantifies purity. Our specification is at least 98%. Check the batch number printed on your vial against the lab reports archive: where a batch has been tested, its report is published there and links to the testing laboratory’s own verification page. If your batch is not listed yet, ask us for its documentation before use; a “typical” certificate is not evidence for a specific vial. See how to read a certificate of analysis.
Storage and shelf life after opening
Store the lyophilised material sealed, dry and protected from light at 2 to 8 °C for routine laboratory use, colder for long-term archiving. After reconstitution with bacteriostatic water, keep refrigerated and use within the window your protocol defines; repeated freeze-thaw cycles degrade peptides. General handling for all our reagents is in the peptide storage protocol.
Regulatory status
Bacteriostatic water for injection is a pharmacy product in several jurisdictions; the material supplied here is a laboratory diluent, not a medicinal product, and is not for human or animal use. Benzyl alcohol has known toxicity considerations in clinical settings, particularly in neonates, which is one more reason this material stays in the laboratory. Research-grade material supplied here is not a medicine and is for in-vitro laboratory use only. The wider framework, including anti-doping status, is described in the peptide risk profile.
Why labs buy BAC Water with their peptides
Batch-numbered vials, published reports where a batch has been tested, shipping from an EU warehouse with tracking (no customs inside the EU) and prices shown with VAT included. Product page: BAC Water 10 ml. Country-by-country sourcing questions are covered in the buyer guide Buy BAC Water in Europe.
References
- Effects of antimicrobial preservatives on protein folding stability and subvisible particle formation. Eur J Pharm Biopharm. 2025. PubMed 40754203
- Banks WA. Peptides and the blood-brain barrier. Peptides. 2015. PubMed 25805003