What is the purest drinking water and is it safe to drink?

September 21, 2025 •

3 min read

By definition, truly pure water is just H₂O, with all other minerals and contaminants removed. When seeking the purest drinking water, options like distilled and deionized water often come to mind, but the distinction and health implications are important to understand for daily consumption.

Quick Summary

The purest form of water available is chemically produced and free of all minerals, often through distillation or deionization, but this is not typically the best choice for daily hydration. For drinking, highly purified water from multi-stage filtration like reverse osmosis is often preferred, as it removes contaminants while some systems add back essential minerals for taste and balance.

Key Points

Distilled is the Purest: The distillation process creates the purest form of water by boiling it and condensing the steam, resulting in water with virtually no dissolved solids.
Deionized Water for Specific Use: Deionized (DI) water has all mineral ions removed and is primarily for industrial or lab applications, not typically for drinking.
Reverse Osmosis for Daily Drinking: An RO system is often considered the best option for purified drinking water, effectively removing contaminants while some systems reintroduce beneficial minerals.
Minerals are Important: While pure in a scientific sense, distilled water is not ideal for long-term drinking as it lacks the essential minerals that a healthy diet and tap water provide.
Total Dissolved Solids (TDS) Gauge Purity: TDS is a key indicator of water purity; however, the source of the solids is more important for health than the amount.
Taste Can Be Affected: The removal of all minerals can give distilled water a bland or 'flat' taste, which is why many prefer remineralized RO water.

Understanding the Concept of 'Pure' Water

In chemistry, a pure substance contains only one type of molecule. For water, this means only H₂O. In reality, all water, including tap and bottled water, contains various dissolved solids, ions, and minerals. Total Dissolved Solids (TDS) is a measure of these substances. While low TDS is often associated with purity, the source of the dissolved solids—whether beneficial minerals or harmful contaminants—is what truly matters for health.

Distilled Water: The Chemical Gold Standard

Distillation is a water purification method that mimics the earth's natural hydrologic cycle of evaporation and condensation. The water is boiled, and the steam is captured and condensed back into a liquid, leaving behind contaminants, minerals, and other dissolved solids. This process results in extremely pure H₂O. For this reason, distilled water is often used in laboratory settings, for medical equipment like CPAP machines, and in appliances where mineral buildup could cause damage.

The Process: Heating water to create steam, which is then re-condensed into liquid water.
Results: Near-total removal of minerals, salts, and contaminants.
Drawbacks: The resulting water can have a 'flat' taste due to the lack of minerals and, for long-term daily drinking, can pose risks of mineral deficiencies if not balanced with diet.

Deionized Water: A Different Approach to Purity

Deionized (DI) water is created by removing all mineral ions (like cations and anions) through an electrically charged process called ion exchange. While it removes ions, it doesn't necessarily remove uncharged organic molecules or microorganisms. For this reason, DI water for consumption should typically undergo additional purification processes like reverse osmosis first. It is primarily used in industrial and scientific applications where the absence of ions is critical.

Reverse Osmosis: A Popular Drinking Water Solution

Reverse osmosis (RO) is a highly effective purification method that uses pressure to force water through a semipermeable membrane. This membrane blocks most dissolved salts, inorganic matter, and large molecules, including many bacteria and viruses. Many multi-stage RO systems combine a pre-filter, RO membrane, and post-carbon filter to remove a wide range of contaminants, including chlorine, pesticides, and heavy metals.

The Reverse Osmosis System

Pre-filtration: Removes larger sediments and chlorine.
Reverse Osmosis Membrane: The core filter that blocks most dissolved solids.
Post-carbon Filter: Polishes the water to remove any lingering tastes or odors.
Remineralization: Some high-end systems add back a balanced blend of minerals for better taste and health benefits.

Comparing Water Purification Methods


Feature	Distilled Water	Deionized Water	Reverse Osmosis (RO) Water
Purity Level	Extremely high; near-zero TDS	Extremely low ion count; may retain uncharged particles	Very high purity; >99% contaminant reduction in good systems
Method	Boiling and condensation	Ion exchange	Pressure through a semipermeable membrane
Removes Minerals?	Yes, completely	Yes, completely removes ionized minerals	Yes, but some systems add them back
Taste	Often described as flat or bland	Bland due to mineral removal	Can be neutral or enhanced with minerals
Use Case	Medical equipment, laboratory, industrial	Laboratory, microelectronics, industrial	Drinking water, cooking, aquariums

The Health Debate: Is the Purest Water the Healthiest?

While distilled and deionized water are the purest in terms of total dissolved solids, this doesn't automatically make them the healthiest option for daily drinking. For long-term consumption, the complete lack of minerals like calcium and magnesium can be a concern, though most people get sufficient minerals from food. The World Health Organization has even noted that water with extremely low concentrations of TDS may have a flat, insipid taste that some find unacceptable. For everyday hydration, purified water with a balanced mineral content is often preferred. Many RO systems on the market offer a final stage that reintroduces beneficial minerals, creating a water that is both clean and pleasant to drink.

Ultimately, the 'best' water depends on your specific needs. If you're using it for a CPAP machine or scientific experiment, the mineral-free nature of distilled water is ideal. For daily drinking, a high-quality, multi-stage reverse osmosis system provides a balance of effective contaminant removal and good taste, and many people find it to be the perfect combination of pure and healthy.

Learn more about water purification techniques at the EPA's website

Frequently Asked Questions

Not necessarily. The 'purest' water, like distilled water, has all minerals removed. While free of contaminants, it also lacks beneficial minerals like calcium and magnesium. For long-term daily consumption, a water that retains or reintroduces these minerals, such as remineralized reverse osmosis water, can be a healthier choice.

While safe for consumption, drinking only distilled water on a long-term basis could lead to mineral deficiencies if you don't get sufficient minerals from your diet. For most people with a balanced diet, it is fine, but it lacks the minerals that often make water taste better and contribute to overall hydration.

Distilled water is created by boiling and condensing steam, which removes virtually everything, including minerals. Reverse osmosis pushes water through a fine membrane to remove contaminants, and many modern systems add back a balanced mineral content. RO is generally preferred for drinking, while distilled water is often used for specific applications like CPAP machines.

You can use a Total Dissolved Solids (TDS) meter, which provides a reading of the total amount of dissolved solids in your water. While useful for checking filter performance, a TDS meter doesn't identify specific contaminants. For a comprehensive analysis, you may need a home water test kit or a lab test.

Purified water, especially from systems with post-carbon filtration and remineralization, often has a cleaner taste because unpleasant odors and contaminants like chlorine have been removed. Distilled water, lacking minerals, can taste bland or 'flat'.

Yes, reverse osmosis water is very safe to drink. The process removes up to 99% of contaminants, including many pesticides, nitrates, and heavy metals. Many modern systems include post-filters to ensure great taste and add back beneficial minerals.

TDS refers to the total amount of inorganic salts and organic matter dissolved in water. It includes minerals like calcium, magnesium, and potassium, as well as potential contaminants. While a high TDS can indicate poor water quality, a low TDS reading simply means there are few dissolved solids present.