Distilled water and bacteriostatic water are both "pure water" in everyday language, and both are clear, colorless liquids. In a laboratory they are different classes of material. Distillation is a purification step; bacteriostatic water is a sterile, endotoxin-controlled, preserved product in a sealed vial. One cannot stand in for the other.
What distillation does and does not do
Distilling water means boiling it and condensing the vapor. Dissolved minerals, salts and most non-volatile impurities stay behind, so distilled water has very low conductivity. Distillation does not, however, produce a sterile product once the water is collected, handled and stored: it is exposed to air, containers and time, all of which reintroduce microorganisms. It carries no specification for bacterial endotoxins, which are heat-stable fragments of Gram-negative bacterial cell walls that accumulate wherever bacteria have grown, including in a carboy of distilled water sitting on a shelf. And it contains no preservative, so any organism that enters it can multiply freely.
What bacteriostatic water is
Bacteriostatic water starts from WFI-grade purified water, is sterilized, has 0.9% benzyl alcohol added as a bacteriostatic preservative, and is sealed in vials of 30 mL or less. Each lot is tested for sterility, for bacterial endotoxins (below 0.5 EU/mL), for pH (4.5 to 7.0), for the preservative content and for particulate matter, and ships with a certificate of analysis. See what is bacteriostatic water.
Side by side
| Property | Distilled water | Bacteriostatic water |
|---|---|---|
| Purification | Distillation | WFI-grade purification, then sterilization |
| Sterile | No | Yes, in the sealed vial |
| Endotoxin limit | None | < 0.5 EU/mL, tested per lot |
| Preservative | None | 0.9% benzyl alcohol |
| Container | Bottles, carboys, jugs | Sealed multi-use vials, 3 to 30 mL |
| Lot-specific COA | Rarely | Yes |
| Repeated use after opening | Not controlled | 28-day convention after first puncture |
| Typical cost per mL | Very low | Higher; reflects testing and packaging |
Where distilled water belongs
Rinsing glassware, filling water baths and autoclaves, preparing non-sterile bench reagents, feeding instruments that specify distilled or deionized water. Anywhere sterility and endotoxin control are not required, distilled water is the economical and correct choice.
Where bacteriostatic water belongs
Anywhere a protocol calls for small, repeated volumes of sterile, endotoxin-controlled water drawn from a single sealed container over a period of weeks: dissolving or diluting lyophilized research materials, preparing dilution series, and similar bench work. Its limitations are the preservative's, not the water's: it is unsuitable for cell culture and for UV-detected analytical methods, where preservative-free sterile water is used instead. See bacteriostatic water vs. sterile water.
Can distilled water be made into bacteriostatic water?
Not in a laboratory setting that needs to rely on the result. Adding benzyl alcohol to distilled water does not sterilize it, does not remove endotoxins, and produces a solution whose preservative concentration and sterility have never been verified. The reasons are covered in can you make bacteriostatic water yourself.
Related comparisons: vs. deionized water, USP water grades explained.
All BAC Water Supply products are supplied for laboratory research use only and are not for human or veterinary use.