Does Filtered Water Have Magnesium? A Guide to Filter Types and Mineral Content

December 24, 2025 •

4 min read

Reverse osmosis filters can remove a significant portion of beneficial minerals like magnesium, but other filtration methods do not. So, does filtered water have magnesium? The amount depends entirely on your specific filtration method and the technology it uses.

Quick Summary

The presence of magnesium in filtered water is determined by the filter technology used. While reverse osmosis removes nearly all minerals, activated carbon and ultrafiltration typically retain them. Some specialized filters can even add minerals back to the water.

Key Points

Filter Type Matters: Different water filters have varying impacts on mineral content; reverse osmosis and distillation remove most minerals, while activated carbon and ultrafiltration retain them.
RO Removes Magnesium: The fine, semipermeable membrane in a reverse osmosis system is designed to block nearly all dissolved solids, including magnesium.
Carbon Filters Retain Minerals: Standard activated carbon filters primarily remove chlorine, organic compounds, and heavy metals, but do not effectively filter out dissolved minerals like magnesium.
Remineralization is an Option: Specialized filters or mineral drops can be used to add beneficial minerals like magnesium back into demineralized water from RO or distillation systems.
Ion Exchange Removes Magnesium: Filters using ion exchange technology, often found in water softeners, deliberately remove magnesium and calcium to address water hardness.
Diet Is the Main Source: While water can contribute to magnesium intake, a balanced diet rich in whole foods remains the primary source for essential minerals.

Understanding Water Filtration and Minerals

Before diving into how different filters affect mineral content, it's important to understand where minerals like magnesium come from. Tap water naturally contains dissolved minerals, which are picked up as water flows over rocks and through the earth. This mineral content is responsible for water's 'hardness' and also contributes to its taste.

Water filtration is the process of removing contaminants and impurities from water. However, the effectiveness and selectivity of this process vary greatly. Some filters are designed to capture a wide range of dissolved solids, while others target specific contaminants, leaving beneficial minerals largely untouched.

Different Filters, Different Outcomes for Magnesium

The technology behind a water filter is the single most important factor determining whether magnesium remains in your drinking water. Below are the most common filter types and their impact on mineral content.

Reverse Osmosis (RO)

Reverse osmosis is a highly effective purification method that forces water through a semipermeable membrane. This membrane has very small pores, allowing water molecules to pass but blocking most larger particles, including dissolved mineral ions like magnesium and calcium. As a result, RO water is very low in mineral content, and while it is highly purified, it can taste 'flat' due to the absence of minerals. Many modern RO systems include a final remineralization stage to add beneficial minerals back to the water for taste and health purposes.

Activated Carbon Filtration

Activated carbon filters are one of the most common types of household water filters, found in pitchers and many under-sink systems. These filters work through a process called adsorption, where contaminants like chlorine, volatile organic compounds (VOCs), and other organic compounds stick to the porous surface of the carbon. Activated carbon is not designed to remove dissolved minerals like magnesium and calcium, so water filtered this way typically retains its mineral content.

Ultrafiltration (UF)

Ultrafiltration uses a semipermeable membrane with slightly larger pores than an RO system. While it effectively removes bacteria, viruses, and other suspended solids, the larger pore size allows dissolved minerals, including magnesium, to pass through. This makes it a good option for those who want to purify their water from biological contaminants while retaining natural mineral content.

Ion Exchange Filters (Water Softeners)

Ion exchange filters are specifically designed to soften water by reducing its mineral content. They use resin beads that attract and replace mineral ions like magnesium and calcium with other ions, typically sodium. This process is highly effective for preventing limescale but also removes the magnesium from the water.

Distillation

Distillation involves boiling water to create steam, which is then condensed back into a liquid form, leaving all minerals and impurities behind. The result is highly pure, demineralized water with extremely low mineral content, including magnesium. Like RO water, distilled water can be remineralized if desired.

The Importance of Magnesium in Your Water

Magnesium plays a crucial role in over 600 biochemical reactions in the body, supporting everything from nerve function to muscle activity and heart health. While food is the primary source of magnesium, the mineral content in drinking water also contributes to daily intake. The magnesium in water is highly bioavailable, meaning the body can absorb it easily. For some individuals, particularly those with dietary restrictions or specific health concerns, water can be a valuable supplemental source of this essential mineral.

Comparing Water Filter Effects on Magnesium


Filter Type	Effect on Magnesium	Typical Cost	Key Consideration
Reverse Osmosis (RO)	Removes 92-99%	High upfront cost	Often requires a remineralization stage for taste and health.
Activated Carbon	Retains most	Low to medium cost	Great for taste/odor removal; leaves minerals intact.
Ultrafiltration (UF)	Retains most	Medium cost	Removes biological contaminants while keeping minerals.
Ion Exchange / Softener	Actively removes	High cost	Designed to reduce hardness, so it removes magnesium.
Distillation	Removes virtually all	Medium to high cost	Provides highly pure, demineralized water.

Retaining or Re-Adding Magnesium to Filtered Water

If you use a filtration method that removes magnesium, like reverse osmosis or distillation, you have options to restore some of the lost mineral content. Many RO systems come with a remineralization cartridge that is added to the final stage of filtration. These cartridges typically contain natural minerals, such as dolomite, which gradually dissolve to add magnesium, calcium, and other minerals back into the water. Alternatively, you can use concentrated mineral drops to add electrolytes and minerals directly to your glass of filtered water. For most people, a balanced diet is sufficient to meet their magnesium needs, but these methods offer a way to supplement intake or simply improve water taste. The National Institutes of Health provides detailed information on dietary magnesium intake and benefits, highlighting its importance for cardiovascular health and bone density.

Conclusion: Making the Right Choice for Your Health

Determining whether filtered water contains magnesium depends on the specific filtration method employed. While systems like reverse osmosis and distillation effectively strip water of minerals, including magnesium, activated carbon and ultrafiltration are designed to leave these beneficial minerals in. For those using mineral-removing filters, options like remineralization cartridges or mineral drops can restore content. Ultimately, the best choice depends on your priorities regarding water purity, taste, and desired mineral intake, which should be considered alongside your overall dietary sources of magnesium.

Frequently Asked Questions

Yes, reverse osmosis (RO) is a highly effective process that removes 92-99% of dissolved minerals, including magnesium, by forcing water through a semipermeable membrane that blocks mineral ions.

Brita filters often use a combination of activated carbon and ion exchange resin. The ion exchange resin is what reduces the minerals responsible for water hardness, like magnesium and calcium, so they do remove some, but not all, magnesium.

For most healthy individuals with a balanced diet, drinking demineralized water is not a major concern, as most essential minerals come from food. However, some studies suggest long-term consumption without supplementation could potentially impact mineral balance.

You can add minerals back to demineralized water using a dedicated remineralization filter cartridge post-RO system, or by adding mineral drops to your drinking water before consumption.

Standard activated carbon filters and ultrafiltration (UF) systems generally do not remove dissolved minerals like magnesium. They primarily target contaminants such as chlorine, organic matter, and bacteria.

Yes, filters that remove high levels of minerals, such as reverse osmosis, can result in water with a 'flat' or neutral taste. Filters that retain minerals, like carbon filters, tend to produce water with a taste closer to the original source.

Filters for pitchers often remove some magnesium. To add it back, you would need to use specific mineral drops or choose a specialized remineralization filter, though this is more common with under-sink RO systems.

While the magnesium in water is bioavailable, your diet is the primary source of this mineral. Water can act as a valuable supplement, but it should not be your only source.