What is filtered water called? Unpacking the Terminology of Clean Water

December 12, 2025 •

4 min read

According to the CDC, filtering tap water can significantly reduce or remove harmful germs and chemicals, and the terminology can be confusing. The simple answer to what is filtered water called is often 'purified water,' though the specifics depend heavily on the filtration process used.

Quick Summary

The term 'filtered water' is a broad category, often used interchangeably with 'purified water.' The specific name, however, depends on the filtration method, such as distillation or reverse osmosis.

Key Points

Broad Term: 'Filtered water' is an umbrella term covering various treatment methods, from basic to advanced.
Purified Water: This term indicates a higher level of filtration, often achieved through reverse osmosis, distillation, or other advanced processes.
Distilled Water: This is water boiled into steam and re-condensed, removing nearly all minerals and impurities but potentially leaving a flat taste.
Reverse Osmosis (RO): A common purification method using a semi-permeable membrane to remove a broad range of contaminants, including heavy metals and dissolved solids.
Mineral Content Matters: Basic filtration retains beneficial minerals, while distillation removes them, and advanced systems may re-add them.
Specific Use Cases: Distilled water is required for sensitive equipment like CPAP machines, while standard filtered or purified water is sufficient for most drinking and cooking.
Testing Water Quality: The type of filter needed depends on the contaminants present in your local water, so testing is recommended.

What is the simple explanation?

At its core, filtered water is any water that has passed through a physical or chemical filter to remove contaminants and impurities. This makes it a very broad, catch-all term. Depending on the level of treatment, filtration is a step in producing water with more specific names, such as purified water, distilled water, or reverse osmosis water. The type of filter used, from a simple carbon pitcher to a complex multi-stage system, determines what is removed from the water. Understanding the specific process is key to understanding the name.

Unpacking the Different Names for Filtered Water

Purified Water

Purified water is a general term for water that has undergone mechanical filtration to remove a significant number of impurities and contaminants. The purification process involves more stringent steps than simple filtering. To be classified as purified water in the U.S., the water must have impurities removed or reduced to extremely low levels, not containing more than 10 parts per million of total dissolved solids. This often includes processes beyond basic carbon filtration, such as reverse osmosis, distillation, or deionization. Bottled water labeled 'purified' commonly uses these methods. Purified water is generally considered safer for drinking and has a higher purity level than standard filtered or tap water.

Distilled Water

Distilled water is a specific type of purified water created through the process of distillation. This involves boiling water and then collecting and condensing the steam back into liquid form in a clean container. The boiling process leaves most contaminants, minerals, and bacteria behind. Due to its high purity and lack of minerals, distilled water is often used in medical settings, laboratories, and household appliances like CPAP machines and steam irons, where mineral buildup is undesirable.

Reverse Osmosis (RO) Water

Reverse osmosis water is another common type of purified water. An RO system forces water under pressure through a semi-permeable membrane with tiny pores. This membrane blocks dissolved solids, such as salts, heavy metals, arsenic, and fluoride, while allowing water molecules to pass through. RO systems are highly effective at removing a broad range of contaminants. They often include additional filters, like activated carbon, to remove chlorine and improve taste. Unlike distillation, some RO systems can be designed to re-mineralize the water, adding back beneficial minerals for taste and health.

Other Filtration Terms to Know

Deionized (DI) Water: This is water that has had almost all of its mineral ions removed using ion-exchange resins. It's primarily used for laboratory or industrial applications.
Spring Water: Water from an underground aquifer that flows naturally to the surface. It's filtered for safety but retains natural minerals.
Softened Water: Water treated to remove hard water minerals (calcium and magnesium), often replaced with sodium ions, to prevent limescale buildup.

Comparison of Common Water Types


Characteristic	Filtered Water (Basic)	Purified Water (Advanced)	Distilled Water	Reverse Osmosis (RO) Water
Filtration Method	Activated carbon, sediment, or mechanical filters.	Multi-stage process, often including RO, distillation, or UV.	Boiling water and condensing steam.	High-pressure forcing water through a semi-permeable membrane.
Level of Purity	Removes some contaminants like chlorine, but leaves others.	Highly pure, with most impurities removed to very low levels.	Extremely pure, with virtually all impurities and minerals removed.	Very high purity, effectively removing a broad range of contaminants.
Mineral Content	Retains beneficial minerals like calcium and magnesium.	Can retain or have minerals added back, depending on the process.	Removes nearly all minerals, which can affect taste.	Removes most minerals but can be re-mineralized.
Taste	Can taste cleaner due to chlorine removal.	Generally clean, can taste better than basic filtered water.	Often tastes flat or bland due to lack of minerals.	Tastes very clean, can be customized with added minerals.
Typical Use	Drinking, cooking, improving taste.	Drinking, cooking, infant formula.	Medical equipment, laboratory use, humidifiers.	Drinking, cooking, aquariums.

Conclusion

While many people simply refer to treated tap water as 'filtered water,' the terminology is more nuanced and depends on the specific treatment it has undergone. The most common alternative names include purified water, distilled water, and reverse osmosis water, each referring to a distinct process and resulting in a different level of purity. For everyday drinking, standard filtered or purified water offers a balance of removing contaminants while retaining beneficial minerals, often improving taste and smell. Distilled and deionized water, on the other hand, are purer but better suited for specific applications where mineral-free water is essential. Ultimately, understanding the different names for filtered water helps you make an informed choice about the quality and purpose of the water you consume or use. For more detailed information on choosing the right filtration system for your needs, the Centers for Disease Control and Prevention (CDC) offers a comprehensive guide.

Types of Water Filters Explained

Activated Carbon Filters: Attract and trap contaminants like chlorine using porous carbon.
Mechanical Filters: Use a physical barrier to block sediment and large particles.
Reverse Osmosis (RO) Filters: Employ a semi-permeable membrane to remove dissolved salts and heavy metals.
UV Filters: Utilize ultraviolet light to kill microorganisms.
Ion Exchange Filters: Replace unwanted mineral ions with others to soften water.

Disclaimer: The information in this article is for general knowledge and informational purposes only and does not constitute medical advice. Consult with a qualified health professional for any health concerns or before making any decisions related to your health or treatment.

Frequently Asked Questions

Filtered water is a general term for water that has undergone some form of filtration, like a carbon filter, to remove certain impurities. Purified water, on the other hand, implies a more rigorous process, often involving reverse osmosis, distillation, or other methods to remove a higher percentage of contaminants.

Yes, distilled water is a type of purified water and therefore can be considered a form of filtered water, though it is a distinct process. It uses boiling and condensation, which is different from standard mechanical filtration.

RO water is produced by a process that forces water through a semi-permeable membrane, filtering out a wide range of dissolved solids, chemicals, and contaminants. It is one of the most effective methods for achieving highly pure drinking water.

Distilled water tastes flat because the distillation process removes not only contaminants but also all the naturally occurring minerals and dissolved gases. These minerals and gases contribute to the characteristic taste of tap or mineral water.

No, not all bottled water is purified. Labels can vary, and some bottled water may simply be treated municipal tap water, while others may be spring water or have gone through specific purification methods. Always check the label for details on the water source and treatment.

Yes, drinking filtered water can offer several health benefits, including reduced exposure to harmful contaminants like chlorine and lead, improved kidney function by reducing toxins, and better skin health. It can also taste and smell better, encouraging better hydration.

In most cases, no. Appliances like CPAP machines and steam irons require distilled water because it is mineral-free, which prevents mineral buildup and damage. Standard filtered or even some purified water may still contain small amounts of minerals that can cause issues.