Why Minerals in Water Actually Matter
The debate about minerals in drinking water often centres on one question: is demineralised (RO-purified) water harmful? The answer requires understanding what minerals water naturally contains, which of those minerals are genuinely beneficial, and what proportion of your daily mineral intake actually comes from water versus food.
The short answer is: water can contribute meaningfully to your intake of calcium, magnesium and a few trace minerals — but food is by far the dominant source of most essential minerals for most people eating a reasonably varied diet. The debate about demineralised water is real but often overstated.
The Beneficial Minerals in Drinking Water
Calcium (Ca²⁺)
The most abundant mineral in the human body — 99% stored in bones and teeth, 1% in blood and soft tissue. Calcium in drinking water is bioavailable (absorbable) at approximately the same rate as dietary calcium.
Bangladesh groundwater calcium levels: Typically 20–150 mg/L depending on geological source.
Daily requirement: 1,000 mg/day for adults. A litre of water with 100 mg/L calcium provides 10% of this requirement — a meaningful but not dominant contribution.
In RO water: Almost completely removed (90–98% rejection). A mineraliser cartridge post-RO can restore 30–80 mg/L.
Health impact of low calcium intake: Long-term inadequate calcium is associated with osteoporosis, hypertension and increased colorectal cancer risk — though dietary calcium from dairy, leafy vegetables and fish is the primary source for most people.
Magnesium (Mg²⁺)
Magnesium is involved in over 300 enzymatic reactions in the body — energy production, protein synthesis, blood glucose control, blood pressure regulation and muscle and nerve function. Magnesium deficiency is genuinely common globally, and water can contribute 10–30% of daily intake in areas with magnesium-rich groundwater.
Bangladesh groundwater magnesium levels: Typically 10–80 mg/L.
Daily requirement: 310–420 mg/day for adults.
Epidemiological evidence: Areas with hard water (high calcium and magnesium) consistently show lower rates of cardiovascular disease mortality in population studies. While the mechanism is debated, the association is robust across many countries and study designs.
The WHO's position: The WHO's 2009 technical report on nutrients in drinking water concluded that water-borne magnesium and calcium contribute meaningfully to reducing cardiovascular disease risk and recommended that water treatment systems should not remove these minerals without replacing them.
Potassium (K⁺)
Present in small amounts in most natural water (1–10 mg/L). Not a significant dietary source — the primary source is food (fruits, vegetables, legumes). Not a concern in either direction for drinking water quality.
Selenium (Se)
A trace mineral with antioxidant properties, important for thyroid function and immune health. Present in very small amounts in groundwater (typically 0.001–0.05 mg/L). Water is a minor source; most selenium comes from food (Brazil nuts, seafood, meat).
Fluoride (F⁻) — the Dual Nature Mineral
Fluoride is the most nuanced mineral in drinking water because the beneficial and harmful ranges are close together.
- Below 0.5 mg/L: Insufficient for dental protective effect
- 0.5–1.5 mg/L: Optimal range — reduces dental caries (cavities) in children and adults
- 1.5–4.0 mg/L: Dental fluorosis — white mottling and pitting of tooth enamel, primarily in children whose teeth are developing
- Above 4.0 mg/L: Skeletal fluorosis — bone damage and joint pain with chronic exposure
Most Bangladesh groundwater fluoride is in the safe range. In some areas, particularly in Sylhet and parts of Rajshahi, elevated fluoride requires RO treatment for removal.
The Harmful Minerals to Watch
Arsenic (As) — No Safe Level
Arsenic is a metalloid (technically not a mineral in the nutritional sense) that occurs naturally in Bangladesh's groundwater at dangerous concentrations across large areas of the country. There is no established safe level of exposure — all arsenic intake contributes to cumulative risk.
Lead (Pb) — No Safe Level
Lead enters water primarily from plumbing — aging lead pipes, lead solder and lead-containing brass fittings are common in older buildings. Lead accumulates in the body over a lifetime. Children are most vulnerable — there is no established safe blood lead level for children.
Nitrate (NO₃⁻)
Naturally present in small amounts but elevated by agricultural fertiliser runoff and sewage contamination. Above 50 mg/L (as NO₃), nitrates are dangerous for infants under 6 months — they cause methemoglobinemia by interfering with blood oxygen transport.
Iron (Fe²⁺/Fe³⁺)
Iron is an essential nutrient but at elevated water concentrations it is more of a nuisance than a health risk for most adults. However, very high iron intake can be concerning for people with haemochromatosis (iron overload disorder). The primary concerns with high iron in water are staining, taste and appliance damage.
Manganese (Mn)
Recent research has elevated concern about manganese in drinking water. Above 0.1 mg/L, manganese is associated with neurotoxic effects — particularly in infants, where elevated manganese exposure during early development is linked to reduced cognitive scores and behavioural problems. The WHO's current health-based guideline of 0.08 mg/L is more restrictive than older standards.
What RO Purification Does to Water Minerals
A standard RO membrane removes 90–98% of all dissolved minerals — beneficial and harmful alike:
| Mineral | % Removed by RO | Health Implication |
|---|---|---|
| Calcium | 90–95% | Reduces water contribution to daily intake |
| Magnesium | 90–95% | Reduces water contribution; may affect cardiovascular benefit |
| Arsenic | 90–97% | Highly beneficial — removes dangerous contaminant |
| Lead | 90–95% | Highly beneficial — removes dangerous contaminant |
| Fluoride | 90–95% | Beneficial in high-fluoride areas; neutral in optimal-range areas |
| Iron | 95–98% | Beneficial — removes taste, staining and appliance damage |
| Nitrate | 85–95% | Highly beneficial — critical for infant formula preparation |
The Practical Recommendation
For households drinking RO-purified water as their primary drinking water source:
- Add a mineraliser or alkaline cartridge post-RO — restores calcium and magnesium to 30–80 mg/L and raises pH to a comfortable 7.0–8.0
- Maintain a varied diet — food provides the vast majority of essential minerals; water contribution is supplementary, not primary
- Do not stop taking RO-purified water over mineral concerns if your source water has elevated TDS, arsenic or other chemical contaminants — the health benefit of removing these contaminants far outweighs the modest reduction in mineral intake
The WHO recommendation is clear: where chemical contamination is present, treatment is essential. Where treatment removes beneficial minerals, restoration through a mineraliser stage is recommended. Both recommendations can be followed simultaneously with a modern multi-stage RO+mineraliser system.