What is the difference between bacteriostatic water and sterile water?

some good reading here

Bacteriostatic Water for Injection, USP is a sterile, nonpyrogenic prepa
ration of water for injection containing 0.9% (9 mg/mL) of benzyl alcohol added as a bacteriostatic preservative, ie. Bacteriostatic water is sterile water which contains a bacteriostatic preservative

Sterile Water for Injection, USP is a sterile, nonpyrogenic preparation of water for injection, which contains no bacteriostat, antimicrobial agent or added buffer. (Nonpyrogenic - will not cause fever)

Sterile water and Bacteriostatic Water are made in special laboratories and are often used as a diluent for injections.

Bacteriostatic Water with isotonic NaCl solution for Injection (the 1ml solvent that comes with HCG amps fromOrganon Pregnyl)

Bacteriostatic 0.9% Sodium Chloride (NaCl) Injection, USP is a sterile, nonpyrogenic, isotonic solution of sodium chloride in water for injection. Each milliliter (mL) contains sodium chloride 9 mg and 0.9% (9 mg/mL) benzyl alcohol added as a bacteriostatic preservative. May contain hydrochloric acid for pH adjustment. It is supplied in an ampoule or a multiple-dose container from which repeated withdrawals may be made to dilute or dissolve drugs for medication. The pH is 5.0 (4.5 to 7.0).

Sodium Chloride, USP is chemically designated NaCl, a white crystalline powder freely soluble in water.
The semi-rigid vial is fabricated from a specially formulated polyolefin. It is a copolymer of ethylene and propylene. The safety of the plastic has been confirmed by tests in animals according to USP biological standards for plastic containers. The container requires no vapor barrier to maintain the proper drug concentration.

Bacteriostatic Sodium Chloride - Clinical Pharmacology
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Sodium chloride in water dissociates to provide sodium (Na+) and chloride (Cl−) ions. These ions are normal constituents of the body fluids (principally extracellular) and are essential for maintaining electrolyte balance.
The distribution and excretion of sodium (Na+) and chloride (Cl−) are largely under the control of the kidney which maintains a balance between intake and output.

The small volume of fluid and amount of sodium chloride provided by Bacteriostatic 0.9% Sodium Chloride Injection, USP, when used only as a vehicle for parenteral injection of drugs, is unlikely to exert a significant effect on fluid and electrolyte balance except possibly in neonates and very small infants.

Water is an essential constituent of all body tissues and accounts for approximately 70% of total body weight. Average normal adult daily requirement ranges from two to three liters (1.0 to 1.5 liters each for insensible water loss by perspiration and urine production).
Water balance is maintained by various regulatory mechanisms. Water distribution depends primarily on the concentration of electrolytes in the body compartments and sodium (Na+) plays a major role in maintaining physiologic equilibrium.

Indications and Usage for Bacteriostatic Sodium Chloride
This parenteral preparation is indicated only for diluting or dissolving drugs for intravenous, intramuscular or subcutaneous injection, according to instructions of the manufacturer of the drug to be admistered

Shelflife

At room temperature [15–30°C (59–86°F)] and in a dark place your unmixed HCG will last for years. Once it is reconstituted it does need to be refrigerated. Reconstituted solution is stable for 60 days when refrigerated.