What Do They Put in Purified Drinking Water?

November 12, 2025 •

4 min read

According to the CDC, bottled water manufacturers may add minerals back to purified water to enhance its flavor and appeal. This might come as a surprise to many who assume purified drinking water is simply plain H₂O. In reality, the purification process can strip water of naturally occurring minerals, leading to a "flat" taste that companies often remedy with flavor-enhancing additives.

Quick Summary

Purified water, stripped of minerals during treatment, is often remineralized by bottlers to improve taste and add health benefits. Common additives include magnesium sulfate, potassium chloride, and calcium chloride, which also help balance pH. Understanding these ingredients provides insight into the contents of both commercial bottled water and home-purified water.

Key Points

Purification Removes Everything: Processes like reverse osmosis strip water of both harmful contaminants and beneficial minerals, resulting in a bland taste.
Minerals Added for Taste and pH: Bottled water companies add trace minerals such as magnesium sulfate and potassium chloride to improve flavor and adjust the pH, creating a crisper, more appealing taste.
Disinfectants Ensure Safety: Municipal water treatment adds disinfectants like chlorine or chloramines to kill pathogens and maintain water safety as it travels through pipes.
Remineralization for Home Users: Home reverse osmosis systems often include a final remineralization filter to restore minerals, counteract the flat taste, and balance pH.
Not all Purified Water is the Same: The specific additives vary by brand and source. Bottled purified water with additives differs significantly from municipally treated water and naturally sourced mineral water.
Source for Nutrition, Not Water: While some minerals are added for health benefits, most nutrition is absorbed from food. Added minerals primarily serve to improve the water's taste.

Purified water is water that has been treated to remove contaminants, such as chemical pollutants, minerals, and microorganisms. The purification process often involves methods like reverse osmosis, distillation, and deionization, which are extremely effective at creating water with a high degree of purity. However, this intensive treatment also removes beneficial minerals, leaving the water with a noticeably bland or 'flat' taste. This is where the practice of adding ingredients back into the water comes into play. For both commercial bottlers and home purification system users, remineralization is key to producing a palatable and sometimes healthier finished product.

The Role of Mineral Additives

Many bottled water companies explicitly list the minerals they add to their purified water. These additives serve several purposes, from improving taste to providing functional health benefits. The minerals are typically added in the form of inorganic salts.

Common Mineral Additives

Magnesium Sulfate: Often listed on bottled water labels, this compound, also known as Epsom salt, is added to purified water to enhance taste. Magnesium is an essential mineral that plays a role in regulating nerve function, blood sugar, and blood pressure.
Potassium Chloride: This is another salt that is frequently used to add flavor and provide the mineral potassium. Potassium is crucial for maintaining fluid balance and normal heart function.
Calcium Chloride: Added to improve taste and reintroduce the mineral calcium, which is vital for strong bones and teeth. The presence of calcium can also help balance the water's pH.
Sodium Bicarbonate: A form of baking soda, this ingredient is added to buffer the pH of the water and enhance the taste profile.

Disinfectants and pH Adjusters

For municipal and large-scale water treatment, chemicals are also used for disinfection and to adjust the water's pH. These agents kill any remaining pathogens and ensure the water quality is stable during transit.

Chemical Disinfectants

Chlorine and Chloramines: Municipal water systems often use chlorine and its compounds as potent disinfectants to kill bacteria and viruses. A residual amount of these chemicals remains in the water to prevent recontamination as it travels through pipes.
Ozone: As an alternative to chlorine, some water treatment plants and bottlers use ozone gas for disinfection. It is a powerful disinfectant that does not leave a noticeable residual taste or odor.
Fluoride: In some regions, fluoride is added to public water supplies to help prevent tooth decay. This is typically done after the main purification steps.

pH Control

Sodium Hydroxide or Lime: For waters with low pH, chemicals like lime or sodium hydroxide are added to increase the alkalinity. This helps prevent corrosion in pipes, especially those containing lead.
Phosphates: Added to reduce the risk of lead from pipes dissolving into the water.

Comparing Water: Purified, Tap, and Mineral

Table: Additives and Treatment Comparison


Feature	Purified Bottled Water	Municipal Tap Water	Natural Mineral Water
Source	Any source (tap, ground, spring), but requires purification.	Surface or ground water.	Underground sources protected from contamination.
Purification Process	Typically reverse osmosis, distillation, or deionization.	Multi-stage filtration and chemical disinfection.	Usually minimal processing; filtered to remove large particles.
Mineral Content	Minerals removed and then strategically added back for taste and function.	Varies greatly depending on the source; not controlled or adjusted for taste.	Contains naturally occurring minerals from its source.
Additives	Calcium chloride, magnesium sulfate, potassium bicarbonate, etc..	Chlorine/chloramines for disinfection, sometimes fluoride and pH adjusters.	Typically none, or only minimal filtration. Preserves the natural mineral content.
Taste	Often described as crisp, clean, or tasteless due to added minerals.	Varies, can have a chemical or mineral taste.	Distinctive taste based on the specific mineral profile of its source.

The Remineralization Debate

For those who purify their own water at home using reverse osmosis (RO) systems, remineralization is a common consideration. An RO system creates highly pure, but demineralized, water. The taste is often described as flat, and some health experts express concern that drinking exclusively demineralized water may have minor health implications, though the body primarily gets minerals from food. Many modern RO systems, such as those from SimPure, include an optional or integrated remineralization stage to add minerals back into the water. The debate centers on personal preference for taste versus the convenience of straight RO water. Home users can add mineral drops or use remineralization filters to restore beneficial minerals like calcium, magnesium, and potassium.

Conclusion

What is put in purified drinking water depends on the source and the producer. For commercially bottled purified water, added minerals and electrolytes are standard for improving taste and creating a consistent product. In contrast, municipal tap water includes disinfectants and pH adjusters to ensure safety during delivery. Ultimately, whether you get your purified water from a bottle or a home system, the final composition is a careful balance of purification and thoughtful re-additives to create a safe, consistent, and palatable product. Consumers who want control over their water's mineral content can opt for a home purification system with a remineralization stage to tailor their drinking experience.

Frequently Asked Questions

Purified water, especially through processes like reverse osmosis, has most minerals removed, which can result in a flat taste. Companies often add a blend of minerals and electrolytes back in to give the water a more distinct, palatable flavor profile.

Not all. While most bottled purified waters have minerals added back for taste, natural mineral or spring waters are sourced from underground and contain naturally occurring minerals that are typically not removed.

For most people, drinking demineralized purified water is not a health concern because the majority of dietary minerals come from food. The World Health Organization (WHO) notes that demineralized water may impact electrolyte balance in some studies, but overall, it is not considered dangerous.

Electrolytes are added to purified water to restore minerals lost during the purification process and to provide functional health benefits, such as enhanced hydration. Common electrolytes include salts of calcium, magnesium, and potassium.

Filtered water typically removes sediment, chemicals, and some bacteria, but often retains natural minerals. Purified water undergoes a more intensive process (like reverse osmosis or distillation) that removes virtually all contaminants and minerals, resulting in a higher level of purity.

Bottled water companies frequently add inorganic salts such as magnesium sulfate, potassium chloride, and calcium chloride to their purified water to improve the taste and mouthfeel.

In certain areas, fluoride is added to public drinking water supplies to help prevent tooth decay and promote strong teeth and bones, a practice supported by many public health organizations.