What is a safe level of magnesium in drinking water?

December 6, 2025 •

3 min read

According to the World Health Organization (WHO), there is no health-based guideline value set for magnesium in drinking water, largely because intake from water is a small portion of total dietary intake. But what is a safe level of magnesium in drinking water for optimal health, and when could it become a concern?

Quick Summary

Safe magnesium levels in drinking water vary, with no single universal standard. Regulations primarily target aesthetic issues like taste, while health risks from water are rare for most individuals. Optimal intake depends on dietary sources, health status, and renal function.

Key Points

No Universal Standard: There is no single universal 'safe' limit for magnesium in drinking water, with guidelines varying globally and largely focusing on taste, not health risk.
Health Risks Are Rare: Magnesium toxicity from drinking water is extremely rare for healthy individuals, as the kidneys efficiently excrete excess amounts.
Kidney Impairment Risk: People with kidney disease are at higher risk of hypermagnesemia from excessive intake, and should monitor all magnesium sources, including water.
Potential Health Benefits: Moderate to high levels of magnesium in drinking water (10-40 mg/L) have been linked to a protective effect against cardiovascular disease.
RO Water Lacks Magnesium: Water treated with reverse osmosis is stripped of most minerals and should be remineralized to restore beneficial elements like magnesium.
Test Your Water: Knowing your local tap water's mineral content is the first step to managing your intake, which can be done via local reports or home test kits.
Dietary Source Is Primary: While water can contribute, most of your magnesium intake comes from food, and supplementation should always be managed with professional guidance.

Understanding Magnesium in Water

Magnesium is an essential mineral naturally present in water sources and contributes to water hardness. For most healthy people, magnesium from drinking water isn't a major health issue and may even offer benefits. However, the 'safe' level is influenced by taste, potential laxative effects, and health conditions, especially kidney function.

Official Guidelines and Standards

No single regulatory standard exists for magnesium in drinking water in the U.S.. Standards often focus on aesthetics rather than health.

World Health Organization (WHO): The WHO has no health-based guideline for magnesium in drinking water, focusing instead on aesthetic issues like taste and hardness.
U.S. Environmental Protection Agency (EPA): The EPA does not regulate magnesium levels. U.S. water supplies typically have less than 20 mg/L.
European Union (EU): Past EU guidelines suggested 30 mg/L for aesthetic reasons, and some member states still provide guidance for taste and corrosion control.
Optimal Ranges: Some research suggests potential heart benefits from water with 10 ppm to 40 ppm or higher magnesium. Other recommendations indicate 20–40 mg/L for health benefits.

Health Effects of Magnesium in Water

Magnesium is crucial for numerous bodily functions. Water is usually a secondary source compared to food, but can be significant for those with low dietary intake.

Potential Risks of High Magnesium

Healthy kidneys efficiently remove excess magnesium, making toxicity from water rare. Risks include:

Laxative Effect: Magnesium sulfate can cause a laxative effect at about 250 mg/L, and a bitter taste around 80 mg/L.
Impaired Kidney Function: Individuals with kidney disease are at risk of hypermagnesemia from high magnesium intake, potentially causing muscle weakness, confusion, or cardiac issues.
Infants: Caution is advised when using water with very high mineral levels for infant formula, though manganese is typically the primary concern.

Benefits of Adequate Magnesium

Many people don't get enough magnesium, and water might help.

Cardiovascular Health: Studies link low magnesium water to higher rates of heart disease. Moderate magnesium levels (10–100 mg/L) in water may reduce this risk.
Bone Health: Magnesium is important for bone density.
Other Benefits: Adequate magnesium is also associated with reduced migraines, better sleep, and lower risk of type 2 diabetes.

How to Manage Magnesium in Your Water

Measuring Magnesium Levels

Check your water's magnesium level using:

Water Quality Reports: Obtain reports from your local water provider.
Home Test Kits: Kits can estimate hardness and sometimes magnesium.
Laboratory Testing: For accuracy, use a certified lab.

Modifying Magnesium Content

Adjust your water's magnesium:

Remineralizing RO Water: RO systems remove minerals. Add remineralization cartridges to restore magnesium.
Mineral Drops: Add concentrated drops to increase mineral content.
Filtering Excess: Ion exchange filters can remove excess magnesium in very hard water.

Comparison of Magnesium in Water Sources


Water Source	Typical Magnesium Range	Primary Considerations
Tap Water (U.S.)	< 20 mg/L	Generally low.
Bottled Mineral Water	Highly variable (up to 1000 mg/L)	Can be a significant source, may cause laxative effects at high levels. Check labels.
Reverse Osmosis (RO) Water	Very low to negligible	Requires remineralization.
Groundwater (Well Water)	Highly variable, can be high (100-150 mg/L)	Can be a significant source depending on location. Test to confirm levels.

Conclusion

There isn't a single safe magnesium level for drinking water; it depends on individual health and diet. For most healthy people, magnesium in water is not a health issue and could offer benefits. The main concerns are taste and hardness. Those with kidney disease should be cautious of high-magnesium water. Testing and filtration options allow for managing water's mineral content. For health information, consult resources like the National Institutes of Health.

Frequently Asked Questions

For most people, the primary risk of high magnesium levels in drinking water is a laxative effect, particularly from magnesium sulfate, and a bitter taste.

No, drinking hard water is highly unlikely to cause magnesium toxicity in healthy individuals. The kidneys can efficiently excrete any excess magnesium ingested from food and water.

The World Health Organization (WHO) does not set a specific health-based guideline for magnesium, as intake from water is not considered a significant health risk for the general population.

You can test magnesium levels in your water by checking your municipal water quality report, using a home test kit, or sending a sample to a certified laboratory for analysis.

Yes, some research suggests that the bioavailability of magnesium from water, where it exists as hydrated ions, may be higher than from food.

Some studies suggest that water with moderate to high magnesium levels (10-40 mg/L) may offer health benefits, particularly for cardiovascular health.

While it's pure, long-term consumption of demineralized water may pose health risks due to the lack of essential minerals like magnesium. It is often recommended to remineralize RO water.