Consumer

Dossier: water softening and public health risks

April 4, 2025

109

Examining the public health implications of water softening, this analysis offers a critical perspective on a widely adopted practice. Beyond the common understanding of its technical advantages, the discussion emphasizes potential risks associated with softened drinking water, including the reduction of essential minerals and increased sodium levels.

This exploration advocates for a precautionary approach to water treatment and suggests a need for re-evaluation of current regulations, such as the EU Drinking Water Directive (EU) 2020/2184 (DWD), to better protect public health by preserving the natural mineral balance of drinking water and ensuring informed consumer choice regarding water quality.

Table of Contents

1. Introduction to water hardness

Water hardness is a natural property of water, primarily determined by the presence of calcium ions and, to a lesser extent, magnesium and other alkaline-earth metals. It is typically expressed in terms of its calcium carbonate (CaCO₃) equivalent.

When hardness exceeds 200 mg/L, it can lead to scale deposits, particularly in heating systems, and increased soap consumption. When heated, hard water tends to form lime deposits, which can reduce the efficiency of water heaters and other appliances.

However, maintaining adequate water mineralization is a public health priority that is often overlooked. Despite its significance, no official guideline value has been established to ensure its protection. This underscores the need to differentiate water treatment strategies based on its intended use — for example, drinking water versus technical water systems.

2. Water softening and its methods

Water softening is a common practice aimed at reducing water hardness, primarily caused by calcium and magnesium ions. The most widespread method employs ion-exchange resins that replace calcium (Ca²⁺) and magnesium (Mg²⁺) ions with sodium (Na⁺) ions. This process occurs through resin beads charged with sodium ions, which swap places with the hardness minerals when water passes through the system.

Alternative methods include:

reverse osmosis systems that force water through semi-permeable membranes;
weakly acidic membrane treatments that remove calcium and magnesium without sodium exchange (though producing CO₂ as byproduct);
template-assisted crystallization that alters mineral structure without removal.

The World Health Organization (WHO) suggests partial treatment approaches, such as softening only hot water lines entering heaters while maintaining mineral-rich cold water for consumption. Some systems incorporate bypass mechanisms or remineralization units to maintain essential mineral content in drinking water.

3. Health risks of water demineralization

Scientific evidence highlights significant concerns for public health about complete water demineralization, as follows.

3.1. Food safety risks

Some ion-exchange resins may release organic contaminants at levels exceeding safety standards
Demineralized water’s increased corrosivity may leach heavy metals from pipes, exposing consumers to harmful contaminants
Excessively soft water (<15°F hardness) in heating systems promotes microbial growth, including Legionella risks.

3.2. Mineral deficiency risks

Reduced intake of calcium and magnesium – essential for bone development, muscle function, nerve transmission and cardiovascular health
Particularly impacts vulnerable groups: lactose-intolerant individuals, those on plant-based diets, and people with specific medical conditions
Potential contribution to mineral imbalances during physiological stress (excessive sweating, fluid loss).

4. The sodium ion problem in softened water

An often-overlooked concern is that ion-exchange softening significantly raises the sodium content of water, leading to several public health issues.

4.1. Sodium intake concerns

EFSA establishes 2.0 g/day as safe sodium intake for adults
Softened water can exceed 300 mg sodium/liter, contributing 600-700 mg/day from water alone
Combined with dietary sodium (particularly from processed foods), this may approach or exceed recommended limits.

4.2. Health implications

Scientific evidence links high sodium intake to increased urinary calcium excretion
Potential bone mineral imbalance, especially in individuals with low calcium intake
Possible exacerbation of hypertension risks, though water-specific evidence remains limited.

4.3. Compliance, and organoleptic issues

Possible violation of EU’s Drinking Water Directive requirements (see paragraph 5)
Sodium levels >200 mg/L often affect water taste, potentially making it unpalatable.

5. The EU‘s Drinking Water Directive

Waters intended for human consumption, under the Drinking Water Directive (EU) 2020/2184 (DWD), include:

all treated or untreated water intended for drinking, cooking, food preparation, or other domestic uses in both public and private premises, regardless of its source — whether supplied through a distribution network, tankers, bottles, or containers, including spring water;
all water used in food businesses for manufacturing, processing, preserving, or placing products or substances on the market for human consumption.

Such water is considered safe and clean if:

it does not contain microorganisms, parasites, or other substances in quantities or concentrations that may pose a potential risk to human health; and
it meets the minimum requirements provided by the EU Directive, Annex I.

5.1. DWD: minimum water hardness

The European Union’s Drinking Water Directive (DWD) sets a minimum total hardness threshold of ≥ 15 °F as a recommended indicator parameter for water undergoing desalination treatments. This level must be maintained through proper blending with other water sources intended for human consumption or by applying suitable remineralization treatments.

The recommended value specifically applies to water leaving desalination and softening plants used within potable water management systems over the medium to long term. It does not apply to water subjected to further treatments downstream of the point of delivery.

This parameter is assessed based on monthly or quarterly averages and should not be exceeded in more than 25% of analytical data collected over a one-year period. If the threshold is exceeded, corrective measures by local health authorities are required, if there is evidence of a health risk.

5.2. Responsibility for water quality

The responsibility for maintaining the quality of water intended for human consumption up to individual user points is assigned to the Internal Water Distribution Manager. Depending on the case, this may include:

the owner, operator, administrator, or director of a facility;
any delegated or contracted entity responsible for the internal water distribution system within public or private premises, covering the section between the point of delivery and the point of use.

For water supplied through an internal distribution system, the Internal Water Distribution Manager must ensure that the parameter values — which are met at the point of delivery — are maintained at the point of use within public and private premises.

5.3. Filtering materials, safety requirements

Chemical reagents, as well as active (e.g., ion-exchange resins) and passive filtering materials used in the treatment, preparation, and distribution of drinking water, must comply with relevant safety and quality standards.

Filtering materials must also be compatible with the water’s characteristics and, under normal or foreseeable conditions of use, must not:

compromise the safety or suitability of water for human consumption, either directly or indirectly;
alter its color, odor, or taste;
promote microbial growth;
release contaminants exceeding acceptable thresholds for the intended treatment.

Authorization for an active filtering material made of ion-exchange and/or adsorbent resin under the Drinking Waters Directive is granted only if it meets substance release requirements based on testing conducted according to EN 12873-3: ‘Influence of materials on water intended for human consumption – Influence due to migration – Part 3: Test method for ion-exchange and adsorbent resins‘.

5.4. Critical issues of water softening systems in healthcare settings

Some members of the Italian Association of Hospital Management Physicians (ANMDO), in Italy, report that water softeners are frequently used in healthcare settings. These systems exchange sodium ions (Na⁺) for calcium (Ca²⁺), magnesium (Mg²⁺), and other bi- and trivalent ions in water. Once depleted, the resins must be regenerated using a saturated sodium chloride (NaCl) solution.

The critical issues associated with water softening systems include:

regeneration of columns with industrial salt, which may contain particulate and biological contaminants;
post-treatment dilution to achieve a water hardness of approximately 10°F, the hotter the water, the greater the calcium sedimentation. Additionally, the softer the water, the more corrosive it becomes to materials.

6. The myth of ‘necessary’ softening: health authorities weigh in

Leading global health institutions — including the World Health Organization (WHO) and the European Food Safety Authority (EFSA) — consistently assert that water softening is not required for health reasons in regions with properly regulated supplies. The Italian Istituto Superiore di Sanità (ISS) reinforces this stance, clarifying that Italian tap water is safe without additional treatment, and softening devices serve primarily to modify taste or reduce limescale — not to eliminate genuine health risks (ISS, 2020; WHO, 2017).

This consensus is critical because demineralized water poses its own dangers:

loss of essential minerals (calcium, magnesium), which contribute to cardiovascular and bone health;
increased sodium intake, linked to hypertension in vulnerable populations;
higher corrosivity, which can leach heavy metals from pipes.

6.1. Balancing water softening and public health

Failure to maintain adequate mineral levels could lead to excessive depletion of essential minerals from drinking water, with the exception of sodium, which is added in exchange for calcium and magnesium ions.

To ensure that drinking and cooking water retain essential minerals and protect public health, the WHO recommends softening only the hot water supply at the inlet of water heaters. This approach reduces costs while preserving the natural mineral balance of non-softened water.

Manufacturers of water softeners may also implement:

a bypass system that allows a portion of untreated water to mix, maintaining essential minerals at consumption points (e.g., kitchen taps);
a remineralization unit installed in the water line before consumption.

While the bypass system helps maintain a proper mineral balance, the remineralization unit does not provide the same level of safety. It cannot fully guarantee a continuous and natural balance of minerals in drinking water, making it a less reliable option from a public health perspective.

6.2. The health benefits of minerals in drinking water

The Italian Istituto Superiore di Sanità (ISS) has emphasized the public health importance of maintaining adequate mineral content, including calcium, in water intended for human consumption. Adequate mineral levels contribute to essential physiological functions and overall well-being. The only exception applies to water used in thermal conditioning systems, where mineral content is not a critical factor (ISS, 2015, 2022).

Mineral intake is also particularly important in certain physiological conditions, such as stress, excessive sweating, or specific illnesses that lead to fluid loss (e.g., persistent vomiting and diarrhea). Calcium plays a crucial role in various bodily functions, including bone tissue development, muscle and myocardial contraction regulation, blood clotting, nerve impulse transmission, and cellular permeability regulation (European Commission, Regulation EU No 432/2012).

Furthermore, the World Health Organization has also suggested a possible positive correlation between hard water and cardiovascular disease prevention (WHO, 2005). Other apparent benefits associated with hard water consumption may be indirectly linked to its lower corrosivity compared to soft water, thereby reducing human exposure to metals leached from pipes and plumbing systems. Both excesses and deficiencies in calcium levels may be associated with adverse effects on the cardiovascular system.

6.3. Misleading marketing

National agencies like the Italian ISS explicitly warn that ‘the only purpose of commercially available water treatment devices, if compliant with regulations, is to modify organoleptic characteristics (taste, odor) or add carbonation – not to ‘make water safer’.

This distinction matters because misleading marketing often frames softeners as ‘health improvements’, when in reality:

no health authority recommends demineralization for general use;
unnecessary softening may violate the precautionary principle, as it removes beneficial minerals while introducing risks (e.g., sodium overload, pipe corrosion).

7. The unnecessary risks of water softening: a precautionary perspective

The EU’s Drinking Water Directive does not mandate softening for public health — instead, it prioritizes maintaining natural mineral balance while ensuring microbial and chemical safety.

However, while the directive addresses technical aspects of water treatment, it largely neglects the public health risks associated with water demineralization. It should therefore be revised in the light of precautionary principle, suggesting:

careful risk-benefit analysis before installing softening systems for potable water
the mandatory information of citizens about water treatment
the individuals’ right to choose un-softened drinking water in whichever context, either public and private.

8. Conclusions and recommendations

Within the fundamental right to access safe water, as outlined by Sustainable Development Goal 6 (#SDG6), lies the inherent right of every individual to choose not to be subjected to forced consumption of softened drinking water.

Given the potential public health risks associated with demineralised water, particularly for vulnerable populations such as individuals with cardiovascular diseases (CVDs), this right to choose un-softened water is paramount.

Ensuring access to naturally mineralised water aligns with the principle of providing safe and healthy water options, allowing individuals to make informed decisions about their consumption based on their specific health needs and preferences.

Dario Dongo

References

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