Is Your Water Actually Helping You Stay Hydrated?
Most hydration content focuses on how much water to drink. Less attention goes to the water itself — what's in it, what's been removed, and whether the mineral content of your water is contributing to or working against your electrolyte balance.
The answer is nuanced and varies significantly by geography, source, and filtration method. But for people who are optimizing their health seriously, understanding the difference between water sources is worth 10 minutes of your time.
Related: Our Experiment Builder can help you apply these ideas. For the complete picture, see our The Complete Guide to Supplement Tracking.
What's in Water (and Why It Matters)
All naturally occurring water contains dissolved minerals — the specific content depends entirely on the geology of the region through which the water flows. The primary health-relevant minerals in water are:
Calcium: Important for bone density, muscle contraction, and nerve signaling. The calcium in mineral water is in ionic form, which has demonstrated bioavailability comparable to or slightly better than calcium from dairy.
Magnesium: Critical for over 300 enzymatic reactions, sleep, and stress response. Populations with higher magnesium levels in drinking water show associations with certain health outcomes in epidemiological research.
Sodium: Present in water at varying levels depending on source. High-sodium well water or softened water contributes meaningfully to daily sodium intake.
Bicarbonate: Functions as a buffer and may support acid-base balance. Higher bicarbonate content in water is associated with mildly alkaline pH.
Fluoride: Added to US municipal water for dental health. Present naturally in some well and mineral waters at varying concentrations.
Silica: Found in volcanic spring waters; some preliminary research suggests a role in aluminum excretion and bone health.
Tap Water
US tap water is among the most tested water sources in the world. Municipal water systems are regulated by the EPA under the Safe Drinking Water Act, and annual consumer confidence reports (CCRs) are publicly available for all municipal systems.
What tap water typically contains:
- Chlorine or chloramine (disinfectants)
- Fluoride (added, typically 0.7ppm)
- Variable minerals depending on source water and local geology
- Disinfection byproducts (DBPs) — compounds formed when chlorine reacts with organic matter
Concerns about tap water:
- Lead contamination in older homes with lead service lines or lead solder — a real problem in specific localities (Flint was the high-profile case, but it's not isolated)
- PFAS ("forever chemicals") — synthetic compounds from industrial and military activity detected in water supplies in many regions
- Disinfection byproducts at high levels — mostly relevant for heavily treated surface water in dense urban areas
How to assess your tap water: Download your municipality's annual CCR. Consider an at-home test kit for lead if your home was built before 1986.
Filtered Water
Filtration quality ranges from basic carbon filtering (Brita) to reverse osmosis (RO) to whole-house systems. The type of filter changes what's removed.
Carbon filters (Brita, ZeroWater carbon stage): Remove chlorine, some DBPs, improve taste. Do not remove fluoride, lead, PFAS, or dissolved minerals.
Reverse osmosis (RO): Removes the widest range of contaminants — fluoride, lead, PFAS, nitrates, most dissolved minerals. This is the gold standard for contamination reduction.
The mineral tradeoff with RO: RO removes essentially all dissolved minerals from the water — including calcium and magnesium. This is a real consideration for people who rely on their water as a mineral source, or for areas where the tap water's mineral content is contributing meaningfully to daily calcium and magnesium intake.
If you use reverse osmosis, consider remineralizing your water with a post-filter remineralization cartridge, or offsetting the lost magnesium and calcium through food and supplements.
A reverse osmosis system with a remineralization stage is a good balance: you get the contamination removal of RO with added back calcium, magnesium, and trace minerals that make the water taste better and contribute to your daily mineral intake. These systems are available for under-sink installation at $200–$400.
Mineral Water
Bottled mineral waters vary more than most people realize. European mineral waters — Evian, San Pellegrino, Gerolsteiner, Vichy — have distinct mineral profiles:
| Brand | Mg (per liter) | Ca (per liter) | HCO3 (bicarbonate) | Sodium |
|---|---|---|---|---|
| Gerolsteiner | 108mg | 348mg | 1816mg | 118mg |
| San Pellegrino | 55mg | 181mg | 215mg | 36mg |
| Evian | 24mg | 78mg | 357mg | 6mg |
| Volvic | 8mg | 11mg | 74mg | 11mg |
| Fiji | 13mg | 18mg | 152mg | 18mg |
Gerolsteiner and San Pellegrino provide meaningful mineral doses — Gerolsteiner in particular delivers approximately 30% of the daily adequate intake for magnesium per liter consumed. Research on Gerolsteiner has examined its role in calcium and magnesium intake in people with dietary deficiencies.
The practical point: If you drink 2 liters of Gerolsteiner daily, you're receiving approximately 216mg of magnesium from your water — a significant fraction of daily needs. If you drink tap water run through RO and don't supplement, your water contributes essentially zero minerals.
What Actually Matters for Most People
If your tap water is clean (confirmed by CCR): Drinking tap water is nutritionally and safety-adequate for most people. A carbon filter improves taste and removes chlorine. This is a fine baseline.
If you have concerns about lead or PFAS: An under-sink RO system is the most effective solution. Add a remineralization stage if you're relying on water for mineral contribution.
If you want to use water as a mineral source: Gerolsteiner or similar high-mineral spring waters are a legitimate way to supplement calcium and magnesium — though they're more expensive than supplements and generate plastic waste if bottled.
If you use RO and don't remineralize: Budget for magnesium supplementation (magnesium glycinate 300–400mg before bed) and ensure calcium intake is covered by diet.
Pros
- +High-mineral water (Gerolsteiner, San Pellegrino) provides measurable calcium and magnesium contributions
- +Reverse osmosis removes the widest range of contaminants including PFAS and lead
- +Understanding your water source and filtration helps you identify mineral gaps to address through diet or supplements
- +Your municipal CCR is publicly available and tells you exactly what's in your tap water
Cons
- -Premium mineral water is expensive ($1–$3/liter) compared to filtered tap water
- -Bottled mineral water generates significant plastic waste at daily consumption volumes
- -RO systems remove beneficial minerals alongside contaminants
- -Water mineral content is a small fraction of daily mineral needs — don't over-optimize this relative to diet
How to Assess Your Current Water Quality
- Download your water utility's CCR — search "[your city] water quality report" or the EPA's ccr.epa.gov portal
- Test for lead if your home has older plumbing — test kits are available for $20–$40
- Look up your area on the EWG tap water database (ewg.org/tapwater) for a consumer-friendly view of detected contaminants
- Note your filtration setup and what it does and doesn't remove
Then match your mineral supplementation approach to the gaps: if your water is high in calcium and magnesium, your supplementation needs may be lower. If you're on RO with no remineralization, account for the missing minerals elsewhere.
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The Bottom Line
For most people with clean, tested tap water, the difference between water sources is more about taste and trace contaminant exposure than dramatic health differences. Where it matters most: if you're using RO filtration, factor the loss of calcium and magnesium into your supplementation strategy. And if you're consuming high-mineral sparkling water regularly, it's contributing more to your magnesium and calcium intake than you might think.