I get asked about purified water almost weekly, usually after a friend notices “purified” on a bottle and wonders if it’s just a fancy word for tap water. After testing dozens of home and commercial systems over the last several years, I can tell you the answer is more specific than most marketing suggests.
Purified water is water that has been mechanically filtered or processed to remove impurities like chemicals, bacteria, viruses, and heavy metals, lowering total dissolved solids (TDS) to 10 parts per million (ppm) or less. That 10 ppm number is the legal threshold set by the U.S. Pharmacopeia, the Environmental Protection Agency, and the FDA for any water labeled “purified.” It is not just marketing.
In this guide, I will break down exactly what “purified” means, how the purification process actually works, and how purified water stacks up against distilled, filtered, and natural mineral water. By the end, you will know when purified water is the right choice and when something else makes more sense.
Table of Contents
What Is Purified Water?
Purified water is any water source, usually tap or groundwater, that has gone through one or more treatment processes to remove chemical and biological contaminants down to very low levels. The U.S. Pharmacopeia defines purified water as containing no more than 10 parts per million of total dissolved solids, with a microbial limit that makes it safe for laboratory and pharmaceutical use.
The term is regulated, but loosely. In the United States, the FDA requires that bottled water labeled “purified” meet the same standards as U.S. Pharmacopeia purified water. NSF International and ANSI run voluntary certification programs that verify bottled water against contaminants like lead, chlorine byproducts, and pesticides.
Here is the part that confuses people most. “Purified” describes a result, not a single process. A water can become “purified” through reverse osmosis, distillation, deionization, carbon filtration, or a combination of these methods. This is why two bottles of purified water can taste slightly different while technically meeting the same standard.
Why the 10 ppm TDS Standard Matters
Total dissolved solids are the measure of all inorganic and organic substances dissolved in water. These include calcium, magnesium, sodium, chloride, and traces of anything else picked up from pipes, soil, or treatment chemicals. Tap water in most U.S. cities runs between 50 and 300 ppm, while purified water must stay under 10 ppm. This is the clearest measurable difference between ordinary tap water and water labeled as purified.
How Is Purified Water Made? The Main Purification Methods Explained
The four primary methods used to purify water at scale are reverse osmosis, distillation, deionization, and carbon filtration. Most commercial systems combine two or more of these for better results.
1. Reverse Osmosis (RO)
Reverse osmosis forces water through a semi-permeable membrane with pores small enough to block most dissolved solids, bacteria, and viruses. The membrane typically removes 95% to 99% of total dissolved solids, along with heavy metals like lead and arsenic. This is the most common method used for bottled purified water and many home filtration systems under the sink.
2. Distillation
Distillation boils water and collects the steam, leaving contaminants behind in the boiling chamber. The steam condenses into liquid form, producing water that is essentially mineral-free. Distillation is one of the oldest purification methods and reliably produces water with TDS below 1 ppm.
3. Deionization
Deionization uses ion-exchange resins to swap hydrogen and hydroxide ions for dissolved mineral ions, stripping the water of salts. This is common in laboratories and aquariums. Deionization alone does not remove bacteria or organic compounds, so it is often paired with another method.
4. Carbon Filtration
Activated carbon filters trap chemical contaminants like chlorine, pesticides, and volatile organic compounds through adsorption. Carbon filtration is rarely used alone to meet the purified water standard, but it is often the final polishing step after reverse osmosis or distillation.
5. Ultraviolet Treatment and Ozonation
UV light and ozone are used as disinfection steps rather than filtration. They neutralize bacteria, viruses, and parasites without changing the chemical makeup of the water. Many commercial bottlers use one of these methods as a final safety layer after filtration.
Purified Water vs Distilled Water
This is the most common comparison question, and the answer is simple: all distilled water is purified, but not all purified water is distilled.
Distillation is one specific way to purify water, using boiling and condensation. Reverse osmosis, deionization, and carbon filtration are other ways that produce water meeting the same 10 ppm TDS standard. The key differences are taste, cost, and energy use. Distilled water often tastes flat because the boiling process removes dissolved gases along with minerals. Purified water made through reverse osmosis can retain slightly more dissolved gases and may taste marginally better to some people.
For most drinking purposes, the two are interchangeable. For specialized uses like CPAP machines or car batteries where mineral deposits cause buildup, distilled water is the safer choice because of its guaranteed 0 ppm mineral content.
Purified Water vs Filtered Water
Filtered water is a broader category than purified water. Filtering usually refers to passing water through a carbon filter or similar media to improve taste and reduce chlorine, sediment, and some heavy metals. Filtering does not necessarily bring TDS below 10 ppm.
A Brita pitcher, for example, is a filter, not a purification system. It reduces chlorine taste and some contaminants, but it does not remove all dissolved solids and does not meet the FDA definition of purified water. Reverse osmosis systems, on the other hand, do meet that standard.
Filtered water is fine for daily drinking if your local tap water already meets safety standards. Purified water offers an extra safety layer when you want mineral content removed, when you are using water for medical devices, or when your local water source has known contamination issues.
Purified Water vs Spring Water
Spring water comes from an underground source that flows naturally to the surface. It is collected at the source and minimally treated, usually just filtered for sediment and disinfected with ozone or UV light. The FDA defines spring water as water collected from a spring, and the water must retain its natural mineral content.
Purified water, by contrast, has had most minerals removed by design. Spring water typically has TDS between 50 and 500 ppm, while purified water stays under 10 ppm. Spring water also has a more variable taste profile depending on the source geology, which is why some brands like Contrex and Vichy have such distinctive flavors, as I explored in my comparison of intensely mineral waters.
For hydration, both are safe. For mineral intake from water, spring water and natural mineral water deliver more calcium, magnesium, and trace minerals like silica, while purified water delivers essentially none. If you care about mineral content from drinking water, purified water is not the right pick.
Is Purified Water Good for You? Health Benefits
For most healthy adults, purified water is safe and offers real benefits. The main advantages are consistency, low contaminant levels, and freedom from chlorine taste and odor.
For people with compromised immune systems, pregnant women, and infants, purified water removes a wider range of pathogens than standard tap water, which can matter when local water quality is uncertain. The Centers for Disease Control and Prevention notes that reverse osmosis systems can remove Cryptosporidium and Giardia, two parasites that are resistant to chlorine disinfection.
There is a persistent myth that purified water “leaches minerals” from your body. This is not supported by current research. Drinking purified water does not strip minerals from your body, because the minerals you absorb come primarily from food, not water. The flat taste some people notice comes from the lack of dissolved minerals and carbon dioxide, not from any chemical reaction inside your body.
Potential Drawbacks of Purified Water
The trade-off for high purity is the loss of beneficial minerals. Drinking only purified water means you get almost no calcium, magnesium, or potassium from your water. For people whose diets are already low in these minerals, this can be a concern over time.
Taste is another drawback. Many people find purified water flat or bland, especially when compared to spring water or mineral water. Adding a slice of lemon or a pinch of mineral salt can help if the taste bothers you.
Environmental impact matters too. Bottled purified water generates plastic waste, and the purification process itself uses energy. Home purification systems are a more sustainable option if you want purified water daily. You can also read more about how purified waters compare on silica content if mineral composition is a concern for you.
Common Uses for Purified Water
Purified water has practical uses beyond just drinking. Here are the most common applications:
CPAP machines and humidifiers: Manufacturers recommend distilled or purified water to prevent mineral buildup in the equipment.
Baby formula: Pediatricians often recommend purified or distilled water for mixing formula, especially for newborns.
Laboratory and medical equipment: Purification removes contaminants that could interfere with experiments or damage sensitive instruments.
Home brewing and aquariums: Brewers and fishkeepers use purified water as a blank slate, then add back the specific minerals they need.
Car batteries and steam irons: Mineral-free water prevents scale buildup that can damage these appliances.
When Should You Choose Purified Water? A Practical Decision Guide
Choose purified water when consistency and low contaminant levels matter more than mineral content. This includes situations where your local tap water has known contamination issues, where you are preparing baby formula, where you use medical equipment that requires mineral-free water, or where you simply prefer the cleaner taste.
Stick with spring water or natural mineral water if you want minerals from your drinking water, prefer a more flavorful taste, or want a more environmentally sustainable option. Mineral water brands also tend to come in glass bottles, which reduces plastic waste.
Consider a home reverse osmosis system if you want purified water daily without the cost and waste of single-use bottles. A typical under-sink RO system costs a few hundred dollars upfront and produces purified water for about 20 to 30 cents per gallon, far less than bottled options over time.
Avoid calling tap water “purified” just because you run it through a basic pitcher filter. To meet the legal purified water standard, the system needs to remove dissolved solids, not just improve taste. Reverse osmosis and distillation are the two most accessible methods for home use that meet the standard.
FAQs
Is purified water good for you?
Yes, purified water is safe and beneficial for most people. It removes contaminants like lead, chlorine byproducts, and pathogens. For healthy adults, the main trade-off is reduced mineral content compared to spring or mineral water, but your body absorbs most minerals from food, not water.
Is purified water the same as distilled water?
No, but they overlap. All distilled water is purified, but not all purified water is distilled. Distillation is one specific purification method that boils and condenses water. Purified water can also be made through reverse osmosis, deionization, or carbon filtration, all of which meet the same 10 ppm TDS standard.
Which is better, purified or spring water?
Neither is universally better. Purified water has lower contaminant levels and fewer minerals. Spring water has more minerals like calcium and magnesium and a more distinctive taste. Choose purified for medical devices or maximum purity. Choose spring for mineral intake and taste.
How do you make purified water at home?
The most reliable home methods are reverse osmosis and distillation. Reverse osmosis systems install under your sink and force water through a semi-permeable membrane, removing 95% to 99% of dissolved solids. Distillation involves boiling water and collecting the condensed steam, which leaves contaminants behind.
What is the healthiest water to drink?
For most healthy people, the healthiest water is whatever safe, clean water you will drink consistently. Both purified and mineral water are healthy options. If you want minerals from water, choose natural mineral water. If you want maximum contaminant removal, choose purified water that meets FDA standards.
Does boiling water purify it?
Boiling kills most bacteria, viruses, and parasites, but it does not remove chemical contaminants, heavy metals, or dissolved solids. Boiled water that has cooled is safer microbiologically but does not meet the legal purified water standard of 10 ppm TDS or less.
Is Brita filtered water the same as purified water?
No. Brita pitchers use carbon filters that reduce chlorine taste and some contaminants, but they do not remove enough dissolved solids to meet the FDA purified water standard. Brita is a filtration system, not a purification system. To meet purified water standards at home, you need reverse osmosis or distillation.
Is purified water safe for CPAP machines?
Yes, purified water is safe for CPAP machines and humidifiers. Manufacturers typically recommend distilled water because it is guaranteed mineral-free, but purified water made through reverse osmosis or distillation also works well and prevents mineral buildup in the equipment.
The Bottom Line on What Purified Water Really Is
What is purified water? In 2026, the answer is straightforward: it is water processed to remove contaminants down to 10 ppm total dissolved solids or less, typically through reverse osmosis, distillation, deionization, or carbon filtration. It is not the same as distilled water (though all distilled is purified), not the same as filtered water (Brita does not meet the standard), and not the same as spring water (which retains natural minerals).
Choose purified water when you need low contaminant levels, mineral-free water for medical devices, or an extra safety layer beyond tap water. Choose spring or mineral water when mineral content and taste matter more than maximum purity. Either way, you are making a better choice than reaching for sugary drinks.
For more detail on how different water types compare on mineral content, check out our guides on silica in bottled water and mineral water taste profiles.