When it comes to water, does “pure” mean the same thing as “sterile”?
Sterile water and distilled water are often used interchangeably. Both are associated with high water quality, and both are used in situations where ordinary tap water may not be suitable. But, the two terms describe very different things.
Distilled water is defined by how it is purified, whereas sterile water is defined by its microbiological status. Distillation involves heating water into vapour and then condensing it back into liquid to remove many dissolved minerals, salts and other impurities. Sterile water, on the other hand, has undergone a sterilisation process designed to eliminate viable microorganisms and is packaged and handled to maintain its sterile status until use.
This difference is especially important when choosing water for medical, laboratory, pharmaceutical or other specialised applications. Distilled water may be highly purified, but that does not automatically mean it is sterile, and sterile water is not necessarily a substitute for every type of purified water.
In this guide, we’ll break down the key differences between sterile water and distilled water, explain how each is produced, where they are commonly used, and what to consider when deciding which type is right for a particular application.
Sterility vs Purity
What Does ‘Sterile’ Actually Tell You?The term sterile relates to microbiological control. Sterile water has undergone a validated process designed to eliminate viable micro-organisms and is packaged under controlled conditions intended to maintain its sterile status until the container is opened. In other words, sterility is a manufacturing and quality-control claim, rather than a general description of how chemically pure the water is. A sterile product has been produced and controlled according to defined requirements, with processes and testing used to demonstrate that the required sterility standard has been achieved. |
What Does ‘Distilled’ Actually Tell You?Distilled describes how the water has been purified. During distillation, water is evaporated and then condensed, leaving many dissolved minerals, salts and other non-volatile substances behind. This can result in water with a low concentration of dissolved solids, making it useful for applications where mineral content matters. But the term “distilled” does not, by itself, guarantee that the finished product is sterile. |
What Is Sterile Water?
Sterile water is water that has been processed so it contains no viable micro-organisms, using a validated method, and then packaged in a way designed to keep it that way until it is opened.
It is important to understand that sterile does not necessarily mean chemically pure. Sterility describes the water’s microbiological status rather than its mineral content, dissolved substances or exact chemical composition.
How Is Water Made Sterile?
Commercial sterile water is produced using a validated sterilisation process appropriate for the product. Depending on the application and manufacturing process, this may involve methods such as
- Thermal Sterilisation: Heat-based sterilisation uses high temperatures, often combined with pressure, to destroy micro-organisms. Unlike simply boiling water at home, commercial sterilisation is monitored, documented, validated and tested to confirm it consistently meets the required standard.
- Sterilising Membrane Filtration: When heat is unsuitable, water may pass through specialised sterilising membrane filters, often with pores around 0.22 microns, to physically remove microorganisms. After filtration, the water must be handled under controlled conditions to prevent contamination.
Why Packaging Matters
These processes, however, do not mean that the water can simply be poured into any container afterwards. Once treated, the sterile water needs to be transferred into an appropriate container and sealed under controlled conditions to protect it from contamination.
The water, container, closure and filling process therefore all play a role in maintaining the product’s sterile status. Once the seal is broken, the water is exposed to its surroundings, which is why sterile water intended for pharmaceutical, laboratory or clinical applications is often supplied in single-use containers and accompanied by specific storage and handling requirements.
What is Sterile Water Used For?
Sterile water is used wherever controlling microbial contamination is an important requirement. Depending on the product and its specification, applications can include laboratory procedures, pharmaceutical preparation, reconstitution and clinical or healthcare procedures that specifically call for sterile water.
The exact requirements can vary considerably between applications, so sterile water should not be treated as a universal product for every situation. The product label, manufacturer’s specifications and relevant professional or laboratory protocols should always determine how a particular product is used.
What Is Distilled Water?
Distilled water is produced through a process called distillation, which uses heat and condensation to remove many dissolved minerals, salts and other impurities from water. It remains widely used in laboratories, manufacturing, healthcare-related applications and everyday household products.
How Is Distilled Water Made?
The basic principle behind distillation is relatively simple: water is heated until it becomes vapour, then cooled so the vapour condenses back into liquid water. Many dissolved minerals, salts and other substances are left behind during this process because they do not evaporate with the water under normal distillation conditions.
In a professional distillation system, the process typically begins with a controlled supply of raw or pre-treated water entering a boiling chamber. Heating elements then raise the water to its boiling point, producing steam. As the steam moves away from the boiling chamber, it passes through a cooling system or condenser, where it loses heat and returns to liquid form.
The resulting distilled water is collected in a dedicated reservoir for storage or distribution. Depending on the system, automated controls can regulate factors such as water levels, temperature and operating conditions throughout the process.
However, this does not mean distillation removes every possible contaminant or guarantees a sterile final product. Some substances can behave differently during evaporation, and the distilled water can also be exposed to contamination during condensation, storage, transfer or handling.
Can Distilled Water Contain Micro-Organisms?
The distillation process itself reduces mineral content, but it does not include the aseptic packaging and handling controls that a sterile product is built around. Contamination can be introduced after distillation, during cooling, storage, decanting or repeated handling, particularly once a container has been opened.
What Is Distilled Water Commonly Used For?
As distilled water contains very few dissolved minerals compared with ordinary tap water, it is useful wherever mineral deposits or dissolved solids could cause problems. Common applications include:
- Steam irons and humidifiers, where reduced mineral content can help minimise scale and deposits
- Some CPAP machines and other equipment, when distilled water is specifically recommended by the manufacturer
- Manufacturing and technical processes that require low-mineral water
- Laboratory applications, such as certain rinsing and preparation tasks where low mineral content is more important than a sterility guarantee
The appropriate water quality ultimately depends on the application. Distilled water should not be assumed to meet the requirements of a process simply because it is highly purified, particularly where a specific sterile or pharmaceutical-grade water specification is required.
Sterile Water vs Distilled Water At A Glance
| Distilled Water | Sterile Water | |
| What it tells you | How the water was purified (evaporation and condensation) | Whether the water is free of viable micro-organisms at manufacture |
| How it’s made | Heated to vapour, then condensed to remove dissolved minerals and salts | Purified and sterilised using a validated method, then aseptically packaged |
| Sterility status | Not guaranteed sterile once produced, packaged or handled | Sterile until the seal is broken, produced under controlled, validated conditions |
| Typical packaging | Bottles, often multi-litre, general retail packaging | Sealed vials or bottles, usually single-use once opened |
| Typical uses | Household appliances, humidifiers, batteries, general lab rinsing | Reconstitution, laboratory and research preparation, clinical protocols requiring a sterile product |
Sterile Water vs Distilled Water in Medical, Pharmaceutical and Laboratory Settings
There is no single definition of “high-quality water” that applies to every situation. Different applications have different requirements, which is why understanding the distinction between sterile and distilled water matters.
Why Sterility Matters In Clinical And Healthcare Settings
In healthcare, microbial contamination can be a significant concern when an application specifically requires sterile water. A product being clean, purified or distilled does not automatically mean it meets a validated sterility requirement.
For this reason, clinical protocols and product instructions specify sterile water when the absence of viable micro-organisms is required. Using the correct product helps ensure the water meets the microbiological requirements established for that particular application.
*This article discusses sterile water and its general applications across laboratory, pharmaceutical, research and clinical settings. It is intended for general information only, rather than instructions for a specific application. Always follow the product’s specifications and the guidance of a qualified healthcare professional or relevant laboratory protocol when using sterile water for a particular purpose.
When Distilled Water Is The Appropriate Choice
Distilled water can be a suitable option for non-sterile applications where low mineral content is the primary requirement, such as certain laboratory rinsing processes, equipment and household appliances where dissolved minerals could cause deposits or interfere with operation. In these situations, the requirement is generally for water with reduced mineral and dissolved-solid content rather than a guarantee of sterility.
What Water Quality Is Required in Pharmaceutical and Laboratory Work?
Pharmaceutical and laboratory environments often have more specific water-quality requirements than simply choosing between sterile and distilled water. Depending on the application, a particular grade or standard may be specified, covering factors such as chemical impurities, microbial content and endotoxins.
Can You Make Sterile Water From Distilled Water At Home?
While water can be distilled or boiled at home, this should not be considered equivalent to commercially manufactured sterile water. Commercial sterile products are produced using validated processes, controlled filling and appropriate packaging designed to establish and maintain the required microbiological status.
A home distillation or boiling setup cannot reliably replicate or verify those manufacturing controls. If a particular application calls for sterile water, the appropriate approach is to use a properly manufactured, sealed sterile water product that meets the required specification.
How Does Bacteriostatic Water Differ?
Sterile and distilled water are not the only types of specialised water you may encounter. Bacteriostatic water is a sterile water product that contains a small amount of a bacteriostatic preservative, commonly benzyl alcohol, which helps inhibit the growth of microorganisms after the container has been opened.
Sterile water is supplied without a preservative and is generally intended for use in a way that maintains sterility, often as a single-use product. Bacteriostatic water, by contrast, is formulated to provide additional protection against microbial growth during repeated withdrawals when used according to its product specifications.
It is often used as a diluent or solvent for certain pharmaceutical preparations, where the specific medication or procedure permits or requires its use. However, the presence of a preservative means it is not suitable for every application or every type of preparation.
The intended use, product label and relevant professional instructions should always determine whether bacteriostatic water is appropriate.
For a more detailed comparison of these products and their intended applications, see our guide to Bacteriostatic Water vs Sterile Water
Storage and Shelf Life: Sterile Water vs Distilled Water
How water is stored can be just as important as how it was produced. Once a container is opened or the water is exposed to its surroundings, there is an increased opportunity for contamination.
- How should sterile water be stored? Sterile water should be kept sealed in its original container, away from direct sunlight, extreme temperatures and potential contaminants. Once opened, the water is exposed to the surrounding environment and its sterile status can no longer be assumed. Always follow the manufacturer’s instructions for storage and use after opening.
- How should distilled water be stored? Distilled water should be kept in a clean, sealed container and protected from contamination. Although distillation removes many impurities, it does not guarantee that the water will remain free from microorganisms after production. Repeated handling, open storage or transferring it to an unclean container can introduce contamination.
Does Sterile Water Expire?
Commercial sterile water has an expiry date for the unopened, sealed product, based on the manufacturer’s validated shelf life. Once opened, the recommended timeframe for use may be much shorter, so always follow the product’s specific instructions.
Can You Substitute One for the Other?
Although sterile and distilled water can share some similarities, they should not automatically be treated as interchangeable. The right choice depends on what the specific application requires.
When in doubt, check the product specifications or speak with the relevant healthcare professional, laboratory professional or manufacturer.
If a product, procedure or laboratory protocol specifically requires sterile water, distilled water should not be used as a substitute unless the relevant instructions say it is suitable. Distillation does not guarantee that the finished product is sterile, so substituting it could introduce a contamination risk.
Sterile water can be used in place of distilled water depending on the application. For general non-sterile applications where low mineral content is the main consideration, sterile water may be suitable, but it can be an unnecessary and more expensive choice.
How to Choose the Right Water Type for Your Application
A short decision framework, in order:
- Identify the intended application: Consider what the water will be used for and whether the application has specific quality requirements.
- Determine what matters most: Does the application require a sterile product, or is low mineral and dissolved-solids content the main consideration?
- Check the instructions or protocol: Manufacturer instructions, laboratory protocols and product specifications should take priority when a particular water type or grade is specified.
- Read the product label: Don’t assume distilled and sterile mean the same thing. Check what the product has actually been manufactured and labelled to meet.
- Ask when the requirements aren’t clear: For healthcare, pharmaceutical or research applications, confirm with a qualified professional or follow the relevant protocol before substituting one type of water for another.
If your preparation work involves sodium chloride solutions as well as water, our guide to Buying Bacteriostatic Sodium Chloride explores what to consider when selecting this type of product.
Conclusion
Sterile and distilled water may serve similar purposes, but the best choice comes down to what your application requires. Distillation focuses on reducing dissolved minerals and impurities, while sterilisation focuses on controlling viable microorganisms.
Before making a selection, review the product’s intended use, quality specifications and handling instructions. If you’re looking for reliable water products for specialised applications, explore the range available from Aussie BacWater or contact our team for help understanding which product may best suit your requirements.
