---
title: "Bacteriostatic Water vs Sterile Water | Primara Labs"
url: https://www.primaralabs.com/resources/bacteriostatic-water-vs-sterile-water
source: Primara Labs, markdown mirror of the HTML page
---

# Bacteriostatic water vs sterile water

Bacteriostatic water is sterile water for injection with benzyl alcohol added as a preservative, supplied in a multiple-dose vial that can be drawn from more than once. Sterile water for injection has no preservative and is labelled single-dose, with the unused portion discarded after the first withdrawal. For a peptide vial that will be drawn from more than once, the preserved water is the one built for the job.

By Primara Labs team · Updated 24 September 2026

## Side by side

What each product's US label says, from the two labels cited below.

*Bacteriostatic water and sterile water for injection, compared from their labels*

| Property | Bacteriostatic water | Sterile water for injection |
| --- | --- | --- |
| Preservative | Benzyl alcohol, 0.9% (9 mg/mL) or 1.1% (11 mg/mL)\[1\] | None: no antimicrobial agent or other preservative\[2\] |
| Container | Multiple-dose, for repeated withdrawals\[1\] | Single-dose vial\[2\] |
| After the first draw | Further draws allowed; see how long below | Discard the unused amount immediately\[2\] |
| Label storage | 20 to 25 °C\[1\] | 20 to 25 °C\[2\] |

The Primara Labs [BAC Water](https://www.primaralabs.com/marketplace/bac-water-3ml) listing describes it as: 3 ml sterile vial, 0.9% benzyl alcohol.

## What the benzyl alcohol does

The Hospira label describes the benzyl alcohol as a bacteriostatic preservative\[1\]. Bacteriostatic means it holds back the growth of bacteria rather than sterilising the solution: it limits what a few organisms carried in on a needle can grow into between draws. It does not make a contaminated vial clean, so it is no substitute for alcohol on the stopper and a new syringe for every entry. The same label warns that benzyl alcohol is not for use in neonates, one of several warnings it carries.

## Why multi-draw vials use BAC water

Every time a needle goes through a stopper there is a chance of carrying microbes into the vial. A reconstituted peptide vial is usually drawn from several times, so the diluent needs something working against growth between those draws. Sterile water has nothing added, and its label treats it as single-dose, discarding what is left after the first withdrawal\[2\]. Bacteriostatic water is made for repeated withdrawals from one container\[1\], and a peptide dissolved in it carries that preservative with it.

## How long an opened vial is used

The Hospira bacteriostatic water label gives no in-use period. CDC guidance, citing USP chapter 797, is that an opened multi-dose vial is dated and discarded within 28 days unless the manufacturer states another date, and never used past its original expiry\[3\]. The US instructions for tesamorelin, a peptide medicine supplied with bacteriostatic water, say to throw away the water left in the bottle 28 days after first use\[4\]. Write the opening date on the water vial the first time it is pierced. For a reconstituted peptide, the peptide's own stability sets the window: follow the lab report or product label. The [storage guide](https://www.primaralabs.com/resources/storing-peptides) covers the rest.

Supplied for laboratory research use only. Not for human consumption. Nothing on this page is medical advice, and nothing here suggests an amount, a frequency or a protocol for any compound.

## Go deeper

-   [Bacteriostatic water in the Philippines](https://www.primaralabs.com/blog/bacteriostatic-water-philippines)
-   [Bacteriostatic water vs sterile water, in depth, on philippinespeptides.com](https://www.philippinespeptides.com/faq/bac-water-vs-sterile)
-   [Bacteriostatic water: sourcing, the 28-day convention, stopper technique, on philippinespeptides.com](https://www.philippinespeptides.com/guides/bacteriostatic-water-philippines)

## Related products

-   [BAC Water 3ml](https://www.primaralabs.com/marketplace/bac-water-3ml)

## Sources

1.  [Bacteriostatic Water for Injection, USP: prescribing information (Hospira)](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=87d6e9dc-fe3b-4593-ac9a-d7493d1959c7). DailyMed, US National Library of Medicine. Cited for benzyl alcohol content, multiple-dose container, label storage and warnings. Checked 24 September 2026.
2.  [Sterile Water for Injection, USP: prescribing information (American Regent)](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=78b35864-4bbc-4759-a5c1-7e4f25e22932). DailyMed, US National Library of Medicine. Cited for single-dose vial, no preservative, discard the unused portion. Checked 24 September 2026.
3.  [Preventing Unsafe Injection Practices](https://www.cdc.gov/injection-safety/hcp/clinical-safety/index.html). US Centers for Disease Control and Prevention. Cited for dating an opened multi-dose vial and the 28-day default, citing USP chapter 797. Checked 24 September 2026.
4.  [EGRIFTA WR (tesamorelin) for injection: US label and instructions for use](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=839334d3-8c1d-4c26-9036-2ab524a6ea75). DailyMed, US National Library of Medicine. Cited for swirl, do not shake; appearance; light; freezing; discard periods on one labelled peptide medicine. Checked 24 September 2026.