How long does bacteriostatic water last?

01

The short answer

Three different clocks:

• Unopened: until the printed expiration date, stored at 20 to 25 °C as the official label directs.
• Opened: date it when first entered and discard within 28 days, unless the manufacturer specifies a shorter or longer date. This is the CDC’s rule for multiple-dose vials in healthcare.
• Any time its sterility is in question: discard it.

The 28-day date is separate from the printed expiration date. The CDC checklist makes that distinction explicitly.

Sources: [1] DailyMed · Bacteriostatic Water for Injection, USP · [3] CDC · Injection Safety Checklist · [4] CDC · Single-dose or multi-dose?

02

Why it outlasts sterile water

Its benzyl alcohol preservative slows the growth of bacteria that enter each time a needle passes through the stopper. Sterile water has no preservative, so its label says single use and discard the rest.

A preservative limits growth; it does not undo contamination. That is why technique matters as much as the date.

Sources: [1] DailyMed · Bacteriostatic Water for Injection, USP · [2] DailyMed · Sterile Water for Injection, USP · [4] CDC · Single-dose or multi-dose?

03

What shortens its life

Each of these adds contamination risk:

• Entering the vial without disinfecting the rubber stopper first. The CDC checklist calls for wiping the septum with alcohol before every puncture.
• Reusing needles or syringes. The CDC standard is a new needle and a new syringe for every entry.
• Storing it outside the labeled temperature range.

Sources: [3] CDC · Injection Safety Checklist · [1] DailyMed · Bacteriostatic Water for Injection, USP

04

When to discard it early

The CDC’s wording for healthcare is to discard a multiple-dose vial whenever its sterility is in question. In practice, labs also discard water that:

• Looks cloudy or discolored, or contains particles.
• Has a damaged stopper, or was left uncapped.
• Has no record of when it was first opened.

Sources: [4] CDC · Single-dose or multi-dose?

05

After it is mixed with a peptide

Once a peptide is dissolved in it, the question changes: how long the solution stays usable depends on the peptide, not the water. Water drives peptide breakdown, which is why peptides ship as dry powder in the first place.

For reconstituted peptides, see how to store peptides.

Sources: [5] Journal of Pharmaceutical Sciences · 1999

06

A simple labeling habit

Write the date on the vial the first time it is entered, along with a discard date 28 days later, or the manufacturer’s date if it differs. Keep one open vial at a time, and note its lot number with your experiment records.

Prism Labs’ bacteriostatic water: What is ?

Sources: [3] CDC · Injection Safety Checklist