What is the purest water to buy?

December 7, 2025 •

4 min read

By one scientific definition, distilled water is the purest form of water available. However, the concept of "purest" can be misleading, as this process also strips water of beneficial minerals. Consumers looking for the cleanest water must weigh extreme purity against the absence of essential electrolytes and the presence of volatile organic compounds.

Quick Summary

This guide examines different types of purified water, comparing production methods like distillation and reverse osmosis. It explains what each removes, discusses the health implications of drinking mineral-free water, and offers a comparison to help you choose the best bottled option for your needs.

Key Points

Distilled is Purest by Definition: Distilled water is the most scientifically pure form, created by boiling and re-condensing steam, which removes virtually all dissolved solids.
RO is Highly Effective Filtration: Reverse osmosis uses a semi-permeable membrane to remove up to 99% of contaminants, but may retain some minerals unless further stripped.
Purity vs. Minerals: Ultra-pure water like distilled lacks minerals, which can affect taste and long-term health if not supplemented by a mineral-rich diet.
Taste Varies by Method: The lack of minerals gives distilled water a flat taste, while re-mineralized RO water and natural spring water often have a more pleasant flavor profile.
Check the Label for Source and Process: Bottled water labels indicate the source (spring, artesian, municipal) and purification method (distilled, RO), which are key to understanding the final product.
Home Systems Offer Customization: Installing a home RO system allows for a continuous supply of purified water, often with the option to add a re-mineralization filter for taste and health benefits.
Different Needs, Different Choices: Choose distilled for specialized uses like medical equipment, and consider RO or naturally mineralized water for daily drinking based on your health and taste preferences.

Understanding the Concept of "Purest" Water

When asking, "what is the purest water to buy?," it's essential to define what "pure" means. For a chemist, pure water is just H₂O, with virtually all dissolved solids and contaminants removed. For a nutritionist, this level of purity can be problematic, as it also removes the beneficial minerals your body uses for hydration. For consumers, it often means water free from any harmful contaminants, like pesticides, bacteria, or heavy metals. The answer to which is "best" depends entirely on your specific needs, whether for medical equipment, laboratory use, or daily drinking.

Distilled Water: The Scientific Gold Standard for Purity

Distilled water is created through distillation, a process that involves boiling water and condensing the steam back into a liquid state. This leaves almost all impurities, including minerals, behind. While this process effectively removes non-volatile contaminants like salts and heavy metals, it is less effective at removing some organic compounds with lower boiling points, such as certain pesticides, which can vaporize along with the water.

Reverse Osmosis Water: A Highly Effective Filtration Method

Reverse osmosis (RO) purifies water by forcing it through a semi-permeable membrane at high pressure. This membrane has extremely small pores that block larger molecules and particles, including dissolved solids, bacteria, and most viruses. While RO removes a high percentage of contaminants, it is not as exhaustive as distillation and often leaves behind some residual minerals. Many modern RO systems include a remineralization stage to add healthy minerals like calcium and magnesium back into the water for better taste and nutritional value.

A Closer Look at the Health and Taste Debate

One of the main arguments against drinking ultra-pure water like distilled water is the removal of essential minerals. Your body primarily gets minerals from food, but water can contribute a small amount. However, drinking demineralized water over the long term, without a sufficiently mineral-rich diet, can lead to concerns about mineral leaching from the body.

The taste is another significant differentiator. Distilled water is often described as having a "flat" or bland taste because the minerals that give water flavor are absent. Conversely, RO water, especially when re-mineralized, often has a crisp, refreshing taste that many people prefer. Water quality standards, like the EPA's recommendation of less than 500 ppm of total dissolved solids (TDS), help ensure safety and taste. A lower TDS level is generally equated with purer water.

Comparison Table: Distilled vs. Reverse Osmosis Water


Feature	Distilled Water	Reverse Osmosis (RO) Water
Purification Method	Boiling water, collecting and condensing steam.	Forcing water through a semi-permeable membrane under pressure.
Purity Level	Removes virtually all dissolved solids, contaminants, and minerals.	Removes 90-99% of contaminants, though some minerals may remain.
Energy Consumption	High energy usage due to the heating and boiling process.	Lower energy consumption compared to distillation, using pressure.
Waste Product	Concentrated impurities left in the boiling chamber.	A significant volume of "brine" or wastewater containing contaminants is flushed away.
Taste	Often described as flat or bland due to the lack of minerals.	Often has a crisp, clean taste, especially with re-mineralization.
Cost	Typically more expensive for home production and often pricier to buy bottled.	Home systems can have a higher initial cost but are more cost-effective per gallon over time.

Other Pure Water Options to Consider

Beyond the two most scientifically pure types, other bottled waters offer a balance of purity, minerals, and convenience. Naturally sourced options include spring water and artesian water, which are collected from underground aquifers and contain a natural mineral composition. Some bottled brands, like Aquafina and Dasani, use reverse osmosis on municipal tap water before adding a precise blend of minerals for taste. Others, such as Smartwater, use a process called vapor distillation followed by the addition of electrolytes. The label is your best guide, so check it to understand the source and purification method.

How to Choose the Best Pure Water for You

Your choice should be based on your personal priorities. If you need water with absolutely no dissolved solids for specific applications, such as for a CPAP machine or scientific use, distilled water is the correct choice. If you are seeking clean, refreshing drinking water with contaminants removed but still want the benefits of minerals, consider an RO system with a re-mineralization filter or certain bottled brands that add electrolytes. For those concerned about plastic waste, investing in a home filtration system, either RO or distillation, is a more sustainable option than relying solely on bottled water. Ultimately, a balanced diet is the primary source of necessary minerals, making safety and taste key factors for daily hydration. You can further investigate the specifics of water quality certifications and testing by consulting resources from the NSF International.

Conclusion: Making an Informed Choice

The question of "what is the purest water to buy" has no single, simple answer. From a technical standpoint, distilled water is the purest, but this level of purification removes both the good and the bad. Reverse osmosis offers a highly effective purification method that is often more practical for daily consumption, especially with re-mineralization. Ultimately, the best choice for you depends on balancing the need for purity against flavor, cost, and the presence of health-supporting minerals. Read labels, understand the purification process, and consider a home system for long-term purity and convenience.

Brand Examples Based on Purification Method

Distilled Water Brands: Nestlé Pure Life, Glaceau Smartwater (vapor distilled).
Reverse Osmosis (RO) Brands: Aquafina, Dasani, Kirkland Signature.
Natural Spring/Mineral Brands: Fiji Water, Acqua Panna, Mountain Valley Spring Water.

Frequently Asked Questions

Distilled water is safe to drink, but because the distillation process removes all minerals, including essential ones, some experts recommend a balanced diet to compensate for the mineral deficiency if consumed over the long term.

Spring water is naturally filtered and often considered pure due to its pristine underground source. However, its purity varies depending on the specific source and may contain a natural composition of minerals and other solids, unlike processed purified waters.

Yes, the semi-permeable membrane in a reverse osmosis system is effective at removing most viruses and bacteria, along with other microscopic contaminants.

Not always. Some major brands, like Aquafina and Dasani, use purified municipal tap water as their source before filtering it with processes like reverse osmosis. However, others, like Mountain Valley, use natural spring sources.

A home filtration system, whether RO or distillation, is generally more environmentally friendly in the long run than repeatedly buying bottled water, as it significantly reduces plastic waste.

You can check the quality of water by using a Total Dissolved Solids (TDS) meter, which provides a numerical value for the concentration of dissolved inorganic solids in the water. Lower TDS generally indicates higher purity.

Studies have shown that plastic bottles can transfer trace amounts of chemicals, such as phthalates, into the water, especially when exposed to sunlight. This is a concern for some consumers who prioritize chemical-free water.