Bacteriostatic water is a preserved, sterile, salt-free diluent in small vials. When one of those four properties is wrong for the work, another product is the better choice. This guide lists the alternatives laboratories actually use and what each one gives up or adds.
The alternatives
| Product | Sterile | Preserved | Ionic content | Choose it when |
|---|---|---|---|---|
| Sterile water (preservative-free) | Yes | No; single use | None | The preservative would interfere, or the whole container is used at once. See vs. sterile water |
| Bacteriostatic sodium chloride (0.9% NaCl + 0.9% benzyl alcohol) | Yes | Yes | 154 mmol/L Na+ and Cl− | A preserved multi-use diluent is wanted and an isotonic salt content is required. See vs. bacteriostatic saline |
| Sterile 0.9% sodium chloride | Yes | No | 154 mmol/L | Salt content required, preservative not wanted. See vs. sterile saline |
| Phosphate-buffered saline (PBS) | Usually, if bought sterile | Usually not (some are supplied with a preservative) | Buffered, about pH 7.4 | pH control matters. See vs. PBS |
| Nuclease-free water | Usually | No | None | Nucleic-acid work, where enzymes rather than microbes are the contaminant of concern. See vs. nuclease-free water |
| Ultrapure (Type I) water from a system | No, unless further treated | No | None; 18 MΩ·cm | Analytical work needing the lowest ionic and organic background. See vs. ultrapure water |
| Buffer with a different preservative system | Varies | Yes | Varies | A preserved diluent is wanted but benzyl alcohol specifically is excluded. See other preservatives |
Deciding quickly
Ask which of the four properties is the problem. If it is the preservative (assay interference, ultraviolet work below 290 nm, cell culture), move to a preservative-free product. If it is the missing salt or buffer, move to the saline or buffered product that matches. If it is the small container, move to sterile water in larger containers. If none of the four is a problem, bacteriostatic water is the right product and the question is only which vial size. See the decision guide.
What is not an alternative
Tap water, distilled water from a benchtop still, deionized water from a cartridge and bottled water are not sterile, not endotoxin-controlled and not preserved, and none of them substitutes for bacteriostatic water in any application that specifies it. See vs. tap and RO water, vs. distilled water and why laboratories buy it sealed.
All BAC Water Supply products are supplied for laboratory research use only and are not for human or veterinary use.