Mixing Water vs sterile water: what's the difference?
by Labdrop
Both are purified water sealed in a vial. Mixing Water contains 0.9% benzyl alcohol, a preservative that stops bacteria growing, so one vial can be used for repeated withdrawals for up to 28 days after it is first opened. Sterile water has no preservative, so a vial is meant for a single use and is discarded once opened.
Side by side
| Mixing Water | Sterile water | |
|---|---|---|
| Contents | Purified water with 0.9% w/v benzyl alcohol | Purified water only |
| Preservative | Yes, benzyl alcohol | None |
| Once opened | Use within 28 days of first piercing the stopper | Single use, discard after opening |
| Also called | Mixing water | Sterile water |
What the benzyl alcohol does
Bacteriostatic means it stops bacteria from multiplying rather than killing them outright. At 0.9%, benzyl alcohol keeps the water in an opened vial usable for multiple withdrawals, which is why Mixing Water is the usual diluent for reconstituting lyophilised laboratory reagents that are used over several days.
Is Mixing Water the same as saline?
No. Saline is a solution of sodium chloride in water. Mixing Water contains no salt. The two are easily confused because both often carry a 0.9% figure, but in saline it refers to sodium chloride and in Mixing Water to benzyl alcohol.
How long does Mixing Water last?
Unopened, until the expiry date on the label. Ours is printed as EXP, 24 months from the fill date. Once the stopper has been pierced, discard the vial after 28 days. Store sealed vials between 2 and 25 °C, away from light.
Which should you use?
Use whichever the method or the reagent's instructions specify. Where a diluent will be drawn from the same vial over several days, a preserved diluent such as Mixing Water is the usual choice. Where a single preparation is made at once, sterile water without a preservative may be specified instead.
See our Mixing Water 10 ml, the Mixing Water FAQ and the rest of our lab reagents.
Labdrop products are laboratory reagents, sold for research and laboratory use only. They are not medicinal products and are not for human or veterinary use.