Sep 1, 2025
Pure Water Isn't Enough
Pure Isn't Enough
Reverse osmosis is the most thorough filtration technology available for drinking water. It removes PFAS, microplastics, heavy metals, pharmaceutical residues, and virtually every dissolved contaminant present in municipal water. It also removes calcium, magnesium, potassium, and bicarbonate — the minerals the body depends on and that water naturally carries. What comes out the other side is clean. Whether it is good depends entirely on what happens next.
What Reverse Osmosis Actually Does
RO filtration works by forcing water through a membrane with pores small enough to reject nearly all dissolved solids. Studies on nanofiltration and reverse osmosis systems report calcium reduction of 43 to 99% and magnesium reduction of 48 to 99%, with RO systems described as removing almost all of both minerals.¹ One analysis of RO-treated school drinking water found that it contributed approximately 0.03% of daily magnesium intake — effectively none.²
The same mechanism that makes RO the most effective contaminant removal technology makes it indiscriminate. It does not distinguish between what belongs in water and what does not.
What the WHO Says About Low-Mineral Water
The World Health Organization conducted a comprehensive review of the health risks associated with demineralized and very low-mineral water. Its conclusions were specific. Consumption of water with total dissolved solids at or below 75 mg/L — the range produced by most RO systems without remineralization — was associated with increased elimination of sodium, potassium, calcium, and magnesium from the body, increased diuresis of approximately 20%, and alterations in fluid-electrolyte balance.³
The same review recommended a minimum TDS of 100 mg/L for drinking water, with an optimal range of 200 to 400 mg/L for standard waters and 250 to 500 mg/L for bicarbonate waters.³ Water with TDS between 25 and 50 mg/L — typical of unremineralized RO output — was described by human volunteers in WHO assessments as simply tasteless.⁴
Why the Minerals in Water Matter
The minerals present in drinking water are not incidental. They are bioavailable — meaning the body absorbs and uses them — and they contribute meaningfully to daily intake, particularly for populations with marginal dietary intake of calcium and magnesium.
Nearly 50% of American adults consume less magnesium than the Estimated Average Requirement based on NHANES data.⁵ Meta-analyses and cohort studies associate higher magnesium concentrations in drinking water with lower cardiovascular disease and coronary heart disease mortality.⁶ Bicarbonate-rich mineral waters have been shown in controlled trials to improve cardiometabolic markers including total cholesterol, LDL cholesterol, and fasting glucose.⁷ A controlled crossover trial confirmed that magnesium from mineral water is as bioavailable as magnesium from food or supplements.⁸
Water is not a passive carrier. Its mineral content is an active variable.
What Remineralization Restores
Remineralization of RO water involves adding back calcium and magnesium salts — typically calcium carbonate and magnesium compounds — along with bicarbonate, to restore hardness, alkalinity, and buffering capacity toward levels found in naturally mineralized water.⁹ The goal is not to add arbitrary minerals but to rebuild a profile that approximates what well-constituted natural water delivers.
WHO assessments and national health agencies including Germany's Federal Institute for Risk Assessment have specifically acknowledged that mineral-poor treated water may warrant remineralization with physiologically appropriate levels of calcium and magnesium to support mineral homeostasis, particularly where dietary intake is already marginal.¹⁰
The Standard RO Gets You Halfway
Removing what does not belong in water is a necessary first step. The research is consistent that pure RO water — stripped of contaminants and minerals alike — is not the destination. WHO's optimal TDS range, the bioavailability data on water minerals, and the documented effects of low-mineral water consumption point in the same direction: the standard is not purity. It is precision.
Filtration establishes a clean foundation. Remineralization is what determines whether the water that comes out is actually good.
Removing contaminants from water is only half the equation. What you rebuild it with is what makes it perform.
Sources
Frontiers in Nutrition — NF and RO Mineral Removal (2024)
PMC / National Library of Medicine — RO Water and Mineral Intake in School Children (PMC11521945)
WHO — Health Risks from Drinking Demineralised Water
WHO — Total Dissolved Solids in Drinking Water Background Document
IMR Press — Global Review of Dietary Magnesium Status
PMC / National Library of Medicine — Magnesium in Drinking Water and CVD (PMC9535516)
ScienceDirect — Bicarbonate-Rich Waters and Cardiometabolic Markers
PMC / National Library of Medicine — Bioavailability of Magnesium from Mineral Water (PMC5642192)
BfR German Federal Institute for Risk Assessment — Health Risk Assessment of Low-Mineral Water
WHO/IRIS — Calcium and Magnesium in Drinking Water Monograph
