Does Water Have More Calcium Than Milk? The Surprising Answer

October 14, 2025 •

3 min read

An 8-ounce glass of milk contains a consistent and concentrated dose of about 300 mg of calcium, a well-known fact for decades. However, with the rising popularity of bottled mineral waters and increased awareness of tap water's mineral content, it's worth exploring the question: does water have more calcium than milk?

Quick Summary

Milk generally contains more calcium per serving than standard tap water, but high-calcium mineral water can rival or even exceed milk's content. Calcium bioavailability from water is often excellent, especially for those avoiding dairy.

Key Points

High-calcium mineral water can have more calcium than milk. Certain brands contain very high concentrations of the mineral, exceeding milk on a per-liter basis.
Milk is a more concentrated and reliable source. An 8-ounce glass of milk offers a consistent 300 mg of calcium, while standard tap water's content is highly variable and often low.
Calcium from water is highly bioavailable. The body can absorb and use the calcium found in mineral water effectively, sometimes even better than calcium from milk.
Hard water contributes to calcium intake. Tap water with high mineral content (hard water) can provide a supplementary source of calcium, although typically much less than milk.
Consider alternative sources if dairy is an issue. For those with lactose intolerance, high-calcium mineral water or fortified plant-based milks are excellent options to meet calcium needs.

The Calcium Content of Milk

Milk is renowned for its high and easily absorbed calcium content. A single cup (8 ounces) of cow's milk provides approximately 300 mg of calcium, depending on the fat content. This consistent concentration has made dairy products a staple recommendation for building strong bones for generations.

Common Dairy Sources of Calcium:

Milk: One cup provides around 276-305 mg.
Yogurt: One cup of plain, low-fat yogurt can offer over 400 mg.
Cheese: One ounce of American cheese contains about 195 mg.
Kefir: A cup of low-fat kefir provides about 317 mg.

While dairy products are excellent calcium sources, they aren't suitable for everyone, particularly individuals with lactose intolerance or milk allergies.

Water's Role as a Calcium Source

Water's calcium content is highly variable and depends on its source. As rainwater filters through rock and soil, it dissolves minerals, including calcium and magnesium. This process is what creates "hard water." The U.S. Geological Survey classifies water based on its hardness, which directly relates to its mineral concentration.

Hard Water vs. Soft Water

Soft Water: Contains low concentrations of minerals, often less than 60 mg/L of calcium carbonate. Its contribution to daily calcium intake is minimal.
Hard Water: Defined by its high mineral content, primarily calcium and magnesium. Moderately hard water can provide 50-75 mg of calcium per 8-ounce glass. While not a health risk, hard water can cause scale buildup in pipes and appliances.

High-Calcium Mineral Water

This is where water's calcium potential shines. Certain mineral waters, sourced from specific geological formations, are naturally rich in calcium and can be a significant dietary source.

Comparison: High-calcium mineral waters like Contrex (468 mg/L) or Gerolsteiner Sprudel (345 mg/L) can provide as much, or more, calcium per liter as milk.
Benefit: These waters offer a calorie-free, lactose-free source of calcium.

Bioavailability: Can Your Body Use Water's Calcium?

For calcium to be beneficial, it must be absorbed by the body. Studies have shown that the bioavailability of calcium from mineral water is at least comparable to, and possibly better than, that from dairy products. This is because the calcium in mineral water is in a dissolved ionic form, which may facilitate absorption. This makes mineral water a valuable option, especially for lactose-intolerant individuals seeking non-dairy calcium sources.

Water vs. Milk Calcium: A Comparative Table


Beverage	Serving Size	Estimated Calcium (mg)	Notes
Whole Milk	1 cup (8 oz)	~276	Consistent, high bioavailability
Low-Fat Milk (1%)	1 cup (8 oz)	~305	Consistent, high bioavailability
Typical Tap Water	1 cup (8 oz)	~5-15	Highly variable depending on location
Moderately Hard Water	1 cup (8 oz)	~50-75	Tap water with high mineral content
High-Calcium Mineral Water (e.g., Gerolsteiner)	~1 cup (8 oz)	~86	Significant source, excellent bioavailability
Calcium-Fortified Orange Juice	1 cup (8 oz)	~349	Added calcium, shake well before serving

The Verdict: So, Does Water Have More Calcium Than Milk?

The definitive answer is: it depends on the water. For standard, everyday drinking, tap water does not have more calcium than milk. However, specific brands of high-calcium mineral water can provide a comparable or even greater amount of calcium per liter than milk.

For an individual's overall dietary strategy, the choice depends on nutritional needs and dietary preferences. For consistent, high calcium intake, milk and other dairy products are reliable. For those who are lactose intolerant or want a calorie-free option, high-calcium mineral water is a valid and effective alternative. In fact, some studies show consuming calcium-rich water can improve bone mineral density. Ultimately, a balanced diet including various calcium sources is the most effective approach for meeting daily requirements.

Conclusion

While milk has long been the gold standard for dietary calcium, the mineral content of water, particularly specific high-calcium mineral waters, offers a surprisingly effective alternative. Standard tap water contributes some calcium but generally far less than milk. The high bioavailability of calcium from water, regardless of the source, ensures it is effectively used by the body. For those with lactose intolerance or those seeking to diversify their nutrient sources, high-calcium water presents a valuable, low-calorie option. Whether choosing milk or water as a primary calcium source, the most important takeaway is to ensure you meet your daily needs through a varied and balanced diet for optimal bone health. For more information, the National Institutes of Health provides comprehensive details on dietary calcium NIH Website.

Frequently Asked Questions

A cup of milk provides significantly more calcium than a typical glass of tap water. Milk contains approximately 300 mg of calcium per cup, whereas standard tap water's calcium content is often much lower and varies by location.

While hard water contributes some calcium to your diet, it is not a sufficient source on its own. Moderately hard water offers 50-75 mg of calcium per 8-ounce glass, but most adults need 1,000 to 1,200 mg per day.

Yes, studies indicate that the calcium in mineral water is well-absorbed by the body, with some research suggesting it is comparable to, or even better than, calcium absorption from milk.

There is no definitive evidence to prove that drinking hard water causes kidney stones. Factors like overall diet, fluid intake, and genetics play a much larger role in kidney stone formation.

Lactose-intolerant individuals can turn to high-calcium mineral water, calcium-fortified plant-based milks, fortified orange juice, leafy greens like kale, and canned fish with bones (like sardines) as excellent sources of calcium.

The calcium in water is in a dissolved, ionic form, whereas calcium in milk is bound in complex compounds. Both are effectively absorbed by the body, but the different chemical states can affect their specific bioavailability.

Signs of hard (high-calcium) water include soap scum, residue on dishes, and mineral scale buildup on faucets and appliances. You can also purchase an at-home water hardness test kit for a more precise measurement.