What it is
Sterile water for injection is water purified to the standard required for injectable medicines, sterilised and sealed, with nothing added: no salt, no preservative, no buffer. It is not a medicine in its own right. Its FDA-approved label gives a single purpose: diluting or dissolving other injectable drugs, following the instructions of the company that makes the other drug.
Because it contains no preservative, it is sold only in single-dose containers, and the label says any unused portion is discarded.
Because it contains nothing dissolved in it, it is far more dilute than blood. If it went straight into a vein on its own, water would rush into red blood cells and burst them, a process called haemolysis. That is why the label is printed with the words “not isotonic” and “hemolytic”.
Sterile Water for Injection, USP is Water for Injection that has been sterilised and packaged in single-dose glass or plastic containers, with no bacteriostat, antimicrobial agent or added buffer. With no solute it is strongly hypotonic relative to plasma. Infused intravenously on its own, it creates an osmotic gradient across the erythrocyte membrane; water enters the cells until they swell and lyse. The label accordingly states that intravenous administration without a solute may result in haemolysis, that the product must be made approximately isotonic before use, and that it should not be used for intravenous injection unless the osmolar concentration of additives gives an approximately isotonic admixture.
The label’s clinical pharmacology section describes water itself: about 70% of total body weight, an average adult daily requirement of two to three litres, and distribution governed largely by sodium concentration. The small volumes used as a pharmaceutical aid are described as unlikely to affect fluid balance except in neonates or very small infants. It has no pharmacological action of its own beyond serving as a solvent and vehicle.
Who made it and when
Sterile water for injection is a pharmacopoeial product, not an invention with a single discoverer. Its quality standard is set by the United States Pharmacopeia, and several companies make and label it.
In the FDA’s records, Hospira’s Sterile Water for Injection, now part of Pfizer, was approved under a new drug application on 27 October 1982, the same day as Hospira’s bacteriostatic water. DailyMed carries labels for sterile water for injection from a number of other labellers.
It sits in a family of similarly named products that are not interchangeable. Bacteriostatic water contains a preservative and is meant for repeated use from one container. Sterile water for irrigation and sterile water for inhalation are made for rinsing and for respiratory equipment respectively, and the irrigation label states plainly that it is not for injection.
Drugs@FDA lists NDA 018801 (Hospira) for Sterile Water for Injection, original approval 27 October 1982, with several container sizes currently marketed on prescription and a 1 mL presentation discontinued. The Hospira label on DailyMed was revised in March 2026. The companion bacteriostatic product, NDA 018802, carries the same approval date.
The related USP articles differ in ways that matter. Bacteriostatic Water for Injection contains 0.9% or 1.1% benzyl alcohol in a multiple-dose container and is contraindicated in neonates; its label directs that where water is needed to prepare medications for neonates, only preservative-free Sterile Water for Injection be used. Sterile Water for Irrigation (for example B. Braun, NDA 016734) is labelled “Not for injection” and warns that it is hypotonic and will cause haemolysis. Sterile Water for Inhalation is a separate USP article, prepared from Water for Injection that is sterilised and suitably packaged with no added antimicrobial agent, and named for inhalation use. The names are similar; the labelled routes are not.
What the data say
There are no efficacy trials of sterile water for injection, and none would make sense. It is a diluent, not a treatment, so there is no condition for it to be tested against.
What exists instead is the safety information on the FDA label. The main hazard is haemolysis if the water enters a vein without enough dissolved substance added to match blood. The label also lists reactions that can come from the water, from the drug added to it, or from the injection itself: fever, tenderness, abscess, tissue damage or infection at the injection site, and vein inflammation or clotting. For newborns and very small infants, the label notes that even the volume of fluid can matter for their fluid and salt balance.
No efficacy trials exist for Sterile Water for Injection, because it is a vehicle with no therapeutic claim; the relevant evidence is the label’s safety content and basic physiology. The label’s adverse reactions section lists febrile response, local tenderness, abscess, tissue necrosis or infection at the injection site, and venous thrombosis or phlebitis extending from the injection site, attributed to the solution, added drugs or technique.
The principal product-specific hazard is haemolysis from intravenous administration of a solute-free, hypotonic fluid; the container statement “NOT ISOTONIC. HEMOLYTIC.” and the contraindication requiring an approximately isotonic admixture both address it. The label states that safety and effectiveness have been established in paediatric patients, with the caveat that in neonates or very small infants the fluid volume may affect fluid and electrolyte balance. Animal reproduction studies have not been conducted, and the label advises use in pregnancy only if clearly needed. Its overdosage section states that the product is to be used only as a diluent or solvent and is unlikely to cause fluid overload except possibly in neonates or very small infants.
Regulatory picture
Sterile water for injection is an FDA-approved prescription product. The approval covers one use: as a diluent or solvent for other injectable drugs, according to those drugs’ own instructions. Mixing a drug into it does not make that drug approved.
Its label makes it single-dose: the container is meant for one use, and anything left over is discarded. This is the practical difference from bacteriostatic water, whose preservative allows repeated withdrawals from one container.
Sterile water sold for irrigation or for inhalation is a different product with a different label, and the irrigation product says plainly that it is not for injection. Pharmacy compounding rules for bulk drug substances do not apply to a finished, approved supply product like this.
Sterile Water for Injection is marketed as a prescription pharmaceutical aid under NDA 018801 and other applications, with a single labelled indication: diluting or dissolving drugs for intravenous, intramuscular or subcutaneous injection according to the drug manufacturer’s instructions. The compounding field is recorded as not applicable because it is a finished approved product, not a bulk drug substance nominated for the 503A list.
FDA’s October 2018 guidance on package-type terms defines a single-dose container as a container of sterile medication for parenteral administration that is not required to meet antimicrobial effectiveness testing requirements and is designed for use in a single patient as a single injection or infusion, with appropriate discard statements on the label. The Hospira label follows that model with “Single-dose” and “Discard unused portion”. By contrast, a multiple-dose container must meet antimicrobial effectiveness testing, which is why the preserved bacteriostatic product exists as a separate article. Irrigation and inhalation grades are separate USP articles with their own labelling, and the irrigation label states that it is not for injection.
