How Long Does Bacteriostatic Water Last After Opening?
An unopened vial lasts until the expiry date printed on its label. Once the stopper has been punctured, the usual limit is 28 days. This guide explains where that number comes from, how sterile water differs, and what shortens the clock.
Research use only. Not for human consumption. Not evaluated by Health Canada. This guide covers specifications, storage and documentation. It gives no dosing or usage guidance.
In short.
- Unopened: good until the printed expiration date, stored as the label directs.
- Opened bacteriostatic water: the common limit is 28 days from the first puncture, unless the label states a different in-use period. It never extends past the printed expiry.
- Opened sterile water: it has no preservative, so it is single-use. The unused portion is discarded once the vial has been opened.
The three cases, side by side.
| Unopened vial | Opened bacteriostatic water | Opened sterile water | |
|---|---|---|---|
| How long it lasts | Until the printed expiry | Usually 28 days from first puncture | Not stored: single use |
| What sets the limit | Manufacturer's expiry date | In-use period, or the expiry date if that comes first | Nothing protects it once opened |
| What to record | Nothing extra | The date of first puncture | Not applicable |
Where the 28 days comes from.
Bacteriostatic water is sterile water with a small amount of benzyl alcohol added as a preservative. The preservative is what makes a vial multi-use: it inhibits the growth of bacteria that may be introduced each time the stopper is punctured.
Two things limit that protection:
- It inhibits growth; it does not sterilize. A vial that has been contaminated is not made clean again by the preservative.
- It is only shown to work for a set period. Preservative effectiveness is typically demonstrated over 28 days, which is why 28 days became the standard in-use limit for opened multi-dose vials.
So the 28-day figure is not the date the water "goes bad". It is the end of the period the preservative can be relied on, assuming the vial has been handled cleanly.
Which date applies: 28 days or the expiry?
Whichever comes first.
- If a vial is opened with a year left before its printed expiry, the limit is 28 days after the first puncture.
- If a vial is opened two weeks before its printed expiry, the limit is the expiry date.
- If the label states its own in-use period, follow the label.
The simplest habit is to write the date of first puncture on the vial the day it is opened. A vial with no opening date on it has no known in-use period, and is better replaced than guessed at. For where the lot code and expiry sit on a vial, see Reading a peptide vial label.
Sterile water: expiration after opening.
Sterile water is a different product, and the answer is different: it does not have a shelf life after opening.
Sterile water contains no preservative. Nothing in the vial stops bacteria from growing once the seal is broken, so it is supplied in single-use containers and the unused portion is discarded after opening. Unopened, it lasts until its printed expiry like any other sealed vial.
That difference is the whole reason bacteriostatic water exists. For a full comparison, see Bacteriostatic vs sterile water.
What shortens the clock.
The 28-day limit assumes a vial in good condition. Replace a vial sooner if:
- the water looks cloudy, discoloured or has particles in it;
- the stopper is damaged, loose or has pieces missing;
- the vial was left uncapped, or the stopper surface was contaminated;
- the opening date is unknown;
- the printed expiry has passed, whatever the opening date.
More punctures also mean more chances for contamination. The limit is the outside edge, not a target.
Does storage change how long it lasts?
Storage keeps a vial within its stated limits; it does not extend them. Store the vial as its label directs, keep it capped, and keep it away from heat and direct light. Refrigerating an opened vial does not add time beyond the in-use period.
The water and the peptide are on separate clocks.
The in-use period above is about the vial of bacteriostatic water. A peptide that has been dissolved in it is a separate question, with its own stability. Vitaliti's stated window for reconstituted vials is up to 30 days refrigerated, and a vial's printed expiry still applies. See How to store research peptides.
Vitaliti's BAC Water.
Vitaliti's BAC Water is a 10ml glass multi-dose vial of bacteriostatic water with 0.9% benzyl alcohol. It is $14.99, and one is included free with a first order using code FIRST. Follow the in-use period and storage directions on its label.