Hub · Bacteriostatic Water
How long does bacteriostatic water last? Unopened, opened and in the fridge
An unopened vial of bacteriostatic water carries the expiry date printed on its lot, a date US rule 21 CFR 211.137 requires manufacturers to set by stability testing. Time limits for opened multi-dose vials come from a separate pharmacy practice standard that CDC reports (CDC, 26 March 2024), and neither record establishes the condition of a research vial. None of the six full labels read states an opened-vial period or a fridge statement.
A jar of jam carries a best-before date on its lid, and you already know the date means something different once the jar is open. Pharmacy water runs on two clocks in the same way. One is printed on the vial by the manufacturer. The other is set by hospital practice and exists because an opened vial can be contaminated.
This page, part of the bacteriostatic water hub, reports both clocks from the labels, CDC and US federal rules, then adds what the sources say about the body's handling of the preservative inside the vial. Storage rules cover temperature and freezing. The page reports records only and gives no directions.
Key facts
| Unopened vial | The manufacturer's printed expiry date, set by stability testing (21 CFR 211.137; CDC, 26 March 2024) |
|---|---|
| Opened vial | A time limit appears only in a pharmacy practice standard, USP General Chapter 797, as reported by CDC on 26 March 2024; the labels read state none |
| Relation to the expiry date | CDC reports that the practice standard's date does not exceed the manufacturer's original expiry date (CDC, 26 March 2024) |
| Refrigerated vial | No figure in any source read; the labels carry a room-temperature statement |
| Expiry fields on the vial | LOT and EXP printed on the vial label; no shelf-life length stated |
| Benzyl alcohol in the body | Oxidised to benzoic acid, conjugated with glycine, excreted as hippuric acid (MMWR, 11 June 1982) |
| Benzyl alcohol half-life | No human figure in the sources read |
| Facts checked | 14 October 2026 |
How long does bacteriostatic water last unopened?
An unopened vial of bacteriostatic water carries the expiry date printed on its lot. US rule 21 CFR 211.137 requires every drug product to bear an expiration date determined by stability testing and related to the storage conditions on its labeling (eCFR, current to 9 October 2026), and CDC's guidance treats the manufacturer's expiration date as the date for an unopened multi-dose vial (CDC, 26 March 2024). The vial label on the manufacturer's record prints lot and expiry fields. None of the six full labels read (8 July 2026, 17 November 2025, 17 November 2025, 10 January 2025, 23 May 2023 and 7 July 2014) states a shelf-life length in months or years, so the printed date is the only figure.
How long does bacteriostatic water last after opening?
No bacteriostatic water label read for this page states a period after opening, and no stability study of the opened water was among the sources (DailyMed, read 14 October 2026). Manufacturer expiry evidence and healthcare handling standards answer different questions. The expiry date rests on stability testing of the product as supplied, while time limits for opened multi-dose vials come from USP General Chapter 797, a pharmacy practice standard that CDC reports (CDC, 26 March 2024). Neither establishes the condition of a research vial. Forum posts, Reddit threads included, are not a source this page uses.
CDC's guidance says a multi-dose vial's preservative gives no complete protection against bacterial contamination (CDC, 26 March 2024), which is why healthcare handling standards for opened vials exist.
How long does bacteriostatic water last in the fridge?
No source read for this page gives a shelf life for bacteriostatic water kept in a refrigerator. The labels carry a room-temperature storage statement and mention no cold storage, so no label-supported figure exists for the fridge (DailyMed, read 14 October 2026). In its paragraph on opened multi-dose vials, CDC names no storage temperature (CDC, 26 March 2024). A one-day survey of 227 opened multi-dose vials of mixed medicines at a 1300-bed hospital in November 2001 recorded that 44 (19%) had been stored in a refrigerator, and because it did not test bacteriostatic water it gives no shelf-life figure (Mattner and Gastmeier, American Journal of Infection Control, 2004).
How long does BAC water last?
BAC water, meaning bacteriostatic water, has two published records and one gap. The records are the manufacturer's printed expiry date for an unopened vial, from 21 CFR 211.137, and an opened-vial time limit in a pharmacy practice standard, USP General Chapter 797 as reported by CDC. The gap is refrigerated or frozen storage, for which no source read gives a figure. The labels read state neither an opened-vial period nor a cold-storage condition (DailyMed, read 14 October 2026).
The table below sets those records beside their sources. Why bacteriostatic water is not simply sterile water explains why the preservative changes the container and the rules.
Does the preservative make an opened vial last longer?
The preservative limits bacterial growth, but it does not remove the risk of contamination or extend the manufacturer's dates. CDC says the preservative in a multi-dose vial gives no complete protection against bacterial contamination, and that the date set for an opened vial does not exceed the manufacturer's original expiration date (CDC, 26 March 2024). A time limit is therefore a handling standard and not a measure of what one vial holds.
Two hospital surveys show what sampling found, and neither tested bacteriostatic water. In a one-day survey of 227 opened multi-dose vials of mixed medicines at a 1300-bed hospital in November 2001, 1 vial and 1 spike were contaminated with Staphylococcus epidermidis, and the survey did not measure infections (Mattner and Gastmeier, American Journal of Infection Control, 2004). In a four-month survey of 637 used multidose vials of mixed medicines at one Iranian teaching hospital, 36 held bacteria, mostly organisms that normally live on people, and the authors wrote that the clinical significance was not resolved (Motamedifar and Askarian, American Journal of Infection Control, 2009). What bacteriostatic water is summarises how those contamination surveys were run and what they sampled.
How fast does the body clear the preservative in bacteriostatic water?
The sources read give a metabolic route for benzyl alcohol but no human half-life. CDC's 1982 MMWR editorial states that benzyl alcohol is normally oxidized rapidly to benzoic acid, conjugated with glycine in the liver and excreted as hippuric acid (MMWR, 11 June 1982). EMA says the body metabolises benzyl alcohol into benzoic acid (EMA, 9 October 2017). The MMWR editors suggested that this pathway may not be well developed in premature infants.
EMA cites Gershanik et al. in the New England Journal of Medicine in 1982 and Brown et al. in The Lancet in 1982 for the gasping syndrome linked to accumulation of benzyl alcohol in newborns, and its document is a regulator's summary of those published reports (EMA, 9 October 2017). The side-effects page sets out those records.
Evidence limits
What is not known about how long bacteriostatic water lasts?
Four things are not known from the sources read. No shelf-life length in months appears on the labels. No stability study of bacteriostatic water after opening was among the sources. No source gives a figure for refrigerated or frozen storage. No human half-life for benzyl alcohol was found. An opened-vial time limit is a pharmacy-practice standard that the labels do not repeat, and a manufacturer may state another date. Each gap means a record on this page is a label statement or a practice standard, not a measured result for a single vial. Records were read on 14 October 2026.
Comparison
Published records for bacteriostatic water vials and where each comes from. Labels are the six full DailyMed bacteriostatic water labels read on 14 October 2026. Not a guide to use.
| Record | Source | On the labels read? | |
|---|---|---|---|
| Unopened vial | The manufacturer's printed expiry date | 21 CFR 211.137; CDC, 26 March 2024 | Expiry field on the vial; no length stated |
| Opened vial | A time limit set by a pharmacy practice standard, which a manufacturer may replace with its own date | USP General Chapter 797 via CDC, 26 March 2024 | No |
| Opened vial, relation to expiry | The practice standard's date does not exceed the manufacturer's original expiry date | CDC, 26 March 2024 | No |
| Refrigerated vial | None found | None found | No; the labels carry a room-temperature statement |
| Frozen vial | None found | None found | No |
FAQ
How long is a punctured bottle of bacteriostatic water good for?
The six full labels read state no period for a punctured vial. Time limits for opened multi-dose vials come from USP General Chapter 797 as CDC reports it (26 March 2024), a practice standard that does not establish the condition of any single vial.
How long does BAC water last on Reddit?
Reddit threads are not a source this page uses. The records here come from CDC, 21 CFR 211.137 and the DailyMed labels, read on 14 October 2026.
How long does bacteriostatic water expire?
Each lot has its own expiry date, set by the manufacturer under 21 CFR 211.137. No label read states a shelf life in months or years.
More in this hub
- Bacteriostatic water vs sterile water: what is the difference?
- What is bacteriostatic water (BAC water)?
- Bacteriostatic water storage: what labels say about the fridge, freezing and expiry
- Bacteriostatic water: US labels, marketing status and Australian rules
- Is bacteriostatic water just sterile water? Label specifications and tests compared
- What is bacteriostatic water used for? What labels and studies report
- Bacteriostatic water side effects: what labels, regulators and studies record
Citations
3 sourcesMattner F, Gastmeier P. American Journal of Infection Control. 2004;32(1):12-16 — bacterial contamination of multiple-dose vials.
doi:10.1016/j.ajic.2003.06.004Motamedifar M, Askarian M. American Journal of Infection Control. 2009;37(9):773-777 — multidose vial contamination in a teaching hospital, Shiraz.
doi:10.1016/j.ajic.2008.12.009Gershanik J et al. New England Journal of Medicine. 1982;307(22):1384-1388 — the gasping syndrome and benzyl alcohol poisoning.
doi:10.1056/NEJM198211253072206
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Read the bacteriostatic water hubForm Laboratories supplies research-use-only reference material. This article is an educational summary of published third-party literature. It is not medical advice, not a use instruction, and research material is not for human or animal use.