Bacteriostatic vs sterile water for reconstitution
When a protocol calls for reconstituting a lyophilised peptide, the solvent is usually water — but not all water is the same. The two you will see most often are sterile water and bacteriostatic water. The distinction matters most when a single vial will be accessed more than once.
Sterile water
Sterile water for injection is purified water that has been sterilised and contains no additives. It is well suited to single-use scenarios where the full reconstituted volume is used promptly, because it brings nothing extra into the solution.
Bacteriostatic water
Bacteriostatic water is sterile water that contains a small amount of a preservative — most commonly 0.9 % benzyl alcohol — which inhibits the growth of bacteria. That preservative is what allows a multi-use vial to be entered repeatedly over a period of time without microbial growth taking hold.
Single use, used immediately → sterile water is fine. Multiple withdrawals from one vial over days → bacteriostatic water is generally preferred because the preservative protects the solution between accesses.
Things to keep in mind
- Some sensitive sequences or specific protocols specify a particular solvent — always defer to the method you are following.
- A few hydrophobic peptides need a small amount of dilute acetic acid to dissolve before water is added.
- Whichever you use, record it in your notes: solvent, volume and date all affect reproducibility.
This is general laboratory handling information for research use only — not medical, clinical or dosing advice.