What Is Sterile Water for Injection (SWFI)?
Sterile water for injection (SWFI) is non-pyrogenic, sterile-filtered water with no preservative additive. It is supplied in single-dose configurations because once exposed to air, the absence of preservative means bacterial growth can begin. SWFI is regulated as a pharmaceutical excipient and is intended for single-use reconstitution applications.
Side-by-Side Specification
| Criterion | Bacteriostatic Water (BW-10) | Sterile Water |
|---|---|---|
| Preservative | 0.9% Benzyl Alcohol | None |
| Use Pattern | Multi-dose (28-day post-puncture) | Single-use only |
| Common Vial Sizes | 10 mL, 30 mL | 5 mL, 10 mL, 50 mL |
| Reconstitution Use | Multi-draw research protocols | Single-event reconstitution |
| Storage After Open | Refrigerate, 28 days max | Discard remainder immediately |
| Cost Per Vial (10 mL) | $9.99 single / $6.49 bulk | Variable |
| Container Standard | Type I Borosilicate Glass | Type I Borosilicate Glass |
When to Use Bacteriostatic Water
Use bacteriostatic water for any research protocol requiring multiple draws from the same reconstituted solution. The 0.9% benzyl alcohol preservative inhibits bacterial growth, allowing continued use across a 28-day window. Most peptide reconstitution research workflows use bacteriostatic water for this reason.
View BAC Water Depot 10 mL specification · single vials from $9.99, bulk from $6.49 per vial.
When to Use Sterile Water
Use sterile water for injection when your protocol specifies a preservative-free diluent, or when only a single reconstitution event is needed and the remaining volume can be discarded. Some research compounds are incompatible with benzyl alcohol — check compound documentation.
Frequently Asked Questions
Can I substitute sterile water for bacteriostatic water in research?
Only if your protocol allows it. Bacteriostatic water permits multi-draw use; sterile water does not. If your reconstitution event is single-use and the remaining volume will be discarded, sterile water is acceptable. For ongoing multi-draw applications, bacteriostatic water is the correct choice.
Does the 0.9% benzyl alcohol in bacteriostatic water affect research compounds?
For most peptide reconstitution applications, 0.9% benzyl alcohol is the established standard and does not interfere. A small number of research compounds specify preservative-free diluents — consult the specific compound's documentation before substitution.
Is one more expensive than the other?
Per-vial pricing is comparable for the same volume. The cost advantage of bacteriostatic water shows in multi-draw workflows where one vial replaces several single-use sterile water vials.
Can both be sourced research-grade?
Yes. Both are available in research-grade specifications. BAC Water Depot supplies research-grade 10 mL bacteriostatic water with ISO 9001:2015 manufacturing and per-lot Certificate of Analysis.
Order Direct
Research-Grade Bacteriostatic Water · From $9.99
ISO 9001:2015 USA-manufactured. Three independent labs verify every production lot. CoA available per lot.
