What is bacteriostatic water?

Sterile water with 0.9 % benzyl alcohol. The preservative inhibits bacterial growth, so the vial can be used several times after opening.

Can I buy bacteriostatic water in a European pharmacy?

Rarely. EU pharmacies usually stock sterile water for injections and saline, neither of which contains a preservative. Bacteriostatic water is sold by laboratory suppliers.

How long does bacteriostatic water last after opening?

Usually about 28 days, refrigerated and handled aseptically.

Can I use sterile water instead?

Yes, but sterile water contains no preservative, so an opened vial is meant for single use.

How much bacteriostatic water do I add to a 10 mg vial?

That depends on the concentration a protocol needs: 2 ml gives 5 mg/ml, 1 ml gives 10 mg/ml.

Bacteriostatic water in Europe: where to buy

Short answer: bacteriostatic water is sterile water with 0.9 % benzyl alcohol. The preservative inhibits bacterial growth, so a vial can be used several times after opening. It is the usual solvent for reconstituting lyophilised research peptides. In most European countries it is not a standard pharmacy product; pharmacies stock sterile water for injection and saline instead.

Bacteriostatic water, sterile water and saline

	Bacteriostatic water	Sterile water for injection	Saline (0.9 % NaCl)
Contents	water + 0.9 % benzyl alcohol	water only	water + sodium chloride
Preservative	yes	no	no
After opening	multiple use, about 28 days refrigerated	single use	single use
Typical use in the lab	reconstituting peptides over several days	peptides that do not tolerate benzyl alcohol	isotonic dilutions

Why it is hard to find in European pharmacies

Bacteriostatic water is a standard product in the US, where it is described in the US Pharmacopeia and sold by manufacturers such as Hospira (Pfizer). In the EU, the European Pharmacopoeia describes water for injections, and that is what pharmacies usually stock, in ampoules or vials. Bacteriostatic water with benzyl alcohol is rarely available there. Laboratory suppliers sell it as a solvent for research use.

Shelf life and storage

Unopened: store cool and protected from light; observe the expiry date.
After the first puncture: usually about 28 days, refrigerated and handled aseptically.
Benzyl alcohol inhibits bacteria but does not reliably kill them. Clean technique is still needed.

Reconstituting peptides

The amount of water sets the concentration: 10 mg of peptide in 2 ml gives 5 mg per millilitre. The water is added slowly along the glass wall of the vial, not sprayed onto the powder, and the vial is swirled gently rather than shaken. Reconstituted peptides are kept refrigerated and protected from light. Details and a calculator (German): Bac Water guide, peptide calculator.

When not to use it

Benzyl alcohol is not suitable for newborns, and some peptides are less stable with it. For these cases sterile water is used instead.

Buying bacteriostatic water in the EU

Peptika ships bacteriostatic water in 3 ml and 10 ml vials from Germany, together with research peptides and without customs clearance inside the EU. Shipping times and rates: Peptides from the EU.