Boron in water: origin, risks, regulations, and treatment

Boron is an element naturally present in rocks, soil, groundwater, and seawater. In drinking water, it can originate from mineral dissolution, saltwater intrusion, desalination, wastewater, certain fertilizers, detergents, and industrial activities. Boron is essential for plant growth, but excessive exposure can cause reproductive and developmental effects in toxicological studies. Its removal is technically challenging because boric acid, the dominant form in many waters, has little electrical charge and passes through certain membranes more easily than other dissolved salts.

Chemical symbol: B
Atomic number: 5
Common form: Boric acid
EU value: 1.5 mg/L

What is boron?

Boron is a chemical element with the symbol B and atomic number 5. It is generally classified as a metalloid because its properties are intermediate between those of metals and non-metals.

In nature, boron rarely exists in its elemental form. It occurs in compounds called borates, notably borax, kernite, colemanite, and ulexite. It can also be incorporated into clays, volcanic rocks, evaporites, and marine sediments.

In water, boron is primarily found as boric acid B(OH)₃ and, as the pH rises, as the borate ion B(OH)₄⁻. This transformation strongly influences its behavior and removal.

Key takeaway: boron is an essential nutrient for plants, but no essential role has been formally established for humans. High and prolonged intake should be avoided.

What are the properties of boron in water?

Characteristic	Information	Importance in water
Symbol	B	Light element of group 13 of the periodic table.
Atomic number	5	Identifies the chemical element.
Common oxidation state	+3	Dominant form in natural boron compounds.
Dominant form at neutral pH	Boric acid B(OH)₃	Molecule with low charge, harder for certain membranes to retain.
Dominant form at high pH	Borate B(OH)₄⁻	Anionic form easier to retain by certain resins and membranes.
Approximate pKa	Approximately 9.2 at 25 °C	Explains the dominance of boric acid in neutral waters.
Volatility	Very low	Boiling is not a reliable removal method.

At pH levels below approximately 9, most dissolved boron exists as non-ionized boric acid. At higher pH levels, the proportion of borate increases, which generally improves its removal via ion exchange or membrane processes.

What is boron used for?

Boron and its compounds are used in numerous industrial and domestic sectors. Borax, boric acid, and borates are the main commercial forms.

manufacturing of borosilicate glass and fiberglass;
ceramics, enamels, and refractory products;
detergents, bleaching agents, and cleaning products;
fertilizers and agricultural products;
wood preservation and authorized biocidal treatments;
metallurgy, welding, and alloys;
electronics and semiconductors;
cosmetics and pharmaceuticals;
flame retardants;
neutron absorption in certain nuclear applications.

These uses can contribute to discharges into wastewater and aquatic environments. In many regions, however, the natural origin remains predominant.

How does boron enter water?

Weathering of rocks and soils

The dissolution of boron-containing minerals is a significant natural source. Groundwater circulating through volcanic, sedimentary, or evaporitic rocks can exhibit high concentrations.

Seawater and saltwater intrusion

Seawater naturally contains several milligrams of boron per liter. Saltwater intrusion into a coastal aquifer can therefore simultaneously increase boron, sodium, and chloride concentrations.

Wastewater

Domestic wastewater can contain boron from detergents, cleaning products, and household use. Boron is sometimes imperfectly removed in conventional wastewater treatment plants.

Agriculture

Some fertilizers and soil amendments contain boron. Excessive application or agricultural drainage can contribute to its presence in surface and groundwater.

Industrial activities

Glass, ceramics, chemical, fiberglass, metal, and electronics industries can discharge boron compounds if effluents are not properly managed.

Geothermal sources

Some geothermal and volcanic waters naturally contain high levels of boron. Their influence can be found in surface waters or local aquifers.

Why is boron important in desalinated water?

Seawater generally contains several milligrams of boron per liter, primarily in the form of boric acid. This neutral molecule is more difficult to retain via reverse osmosis than highly charged ions like sodium or sulfate.

A desalination plant may therefore produce water that is very low in salts while still retaining a significant fraction of the initial boron. To reach a low value, it is often necessary to use a second membrane pass, increase the pH before treatment, or add a selective resin.

The European directive provides a general parametric value of 1.5 mg/L, but authorizes a value of 2.4 mg/L when desalinated water is the predominant source for the network or when geological conditions lead to high levels in groundwater.

Remineralizing desalinated water does not remove remaining boron. It mainly corrects the water's pH, alkalinity, hardness, and corrosive stability.

Why is boron monitored for irrigation?

Boron is a micronutrient essential for plants, but the gap between the useful quantity and the toxic quantity can be small for some species.

Sensitive crops may exhibit marginal burning, yellowing, leaf drop, stunted growth, or reduced yields when irrigation water is too high in boron.

Citrus fruits, avocado, certain fruit trees, and several ornamental plants are particularly sensitive. Other crops are more tolerant.

Water that is compliant for human consumption is therefore not automatically suitable for all crops. Agricultural assessment depends on boron concentration, salinity, soil, drainage, climate, and the plant's sensitivity.

When well water is used for both drinking and irrigation, request an analysis tailored to both uses. Agronomic thresholds may be lower than health-based drinking water values.

What are the health effects of boron?

Ingested boron is rapidly absorbed by the digestive system, distributed throughout the body, and then primarily eliminated by the kidneys. Boric acid and soluble borates turn into similar species in biological fluids.

High acute exposure

Ingestion of large quantities can cause nausea, vomiting, abdominal pain, diarrhea, skin irritation, general weakness, and, in severe cases, neurological or renal damage.

Chronic exposure

The critical effects used for health assessment primarily concern male reproduction and development. These have been observed in animals at doses significantly higher than standard population intake.

Renal elimination

Since boron is mainly eliminated by the kidneys, reduced kidney function may affect its clearance. However, reference values incorporate uncertainty factors designed to protect sensitive populations.

In the event of high concentrations in a well, infants, pregnant women, and people with kidney disease should follow the recommendations of health authorities or their healthcare professional.

Why are reproduction and development studied?

The main toxicological studies have highlighted, at high doses, effects on the testicles, sperm production, and fetal development in animals.

The WHO established its guideline value of 2.4 mg/L based on data related to developmental toxicity. Health Canada established a higher calculated health value but set a maximum acceptable concentration of 5 mg/L, taking treatment feasibility into account.

These effects do not mean that one-time exposure slightly above a guideline value will necessarily cause harm. Recommendations are designed to protect against daily consumption over an entire lifetime.

The risk depends on the total dose from water, food, and other sources. In most situations, diet represents a significant portion of boron exposure.

Is boron carcinogenic?

Available health assessments do not consider common boron compounds to be established carcinogens via ingestion. Animal studies have not provided convincing evidence of a carcinogenic effect under the evaluated conditions.

The values applicable to drinking water are therefore primarily based on non-carcinogenic effects, notably reproductive and developmental toxicity.

The lack of a carcinogenic classification does not mean high exposure is without risk. Reproductive and developmental effects alone justify monitoring boron.

What are the environmental effects of boron?

Boron is naturally present in soil, water, and sediment. It can be transported in dissolved form and does not degrade, as it is a chemical element.

At low concentrations, it is necessary for plant growth. At high concentrations, it becomes phytotoxic and can damage crops, terrestrial vegetation, and certain aquatic organisms.

In arid regions, boron can accumulate in irrigated soils when evaporation is high and drainage is insufficient. Wastewater reused for irrigation must therefore be monitored.

Its mobility depends on pH, soil texture, organic matter, and adsorption onto clays and aluminum or iron oxides.

What are the reference values for boron in drinking water?

Organization or regulation	Value	Interpretation
World Health Organization	2.4 mg/L	Health guideline value based on developmental effects.
European Union – Directive (EU) 2020/2184	1.5 mg/L	General parametric value for water intended for human consumption.
EU – desalinated water or specific geological context	2.4 mg/L	Value applicable when conditions specified by the directive are met.
France	1.5 mg/L	Quality limit aligned with the European framework, with specific regulatory possibility.
Canada	5 mg/L	Maximum acceptable concentration for total boron, based on treatment feasibility.
United States – EPA	5 mg/L	Non-regulatory lifetime health advisory; no specific federal MCL.
Australia	4 mg/L	National health guideline value.

For water distributed in France, the general reference value to consider is 1.5 mg/L. A value of 2.4 mg/L may apply in the situations provided for desalinated water or in certain regions with high natural geological content.

How to analyze boron in water?

Boron can be measured by inductively coupled plasma mass spectrometry (ICP-MS), inductively coupled plasma optical emission spectrometry (ICP-OES), atomic absorption, or validated colorimetric methods.

For compliance assessment, total boron is generally measured. In clear water, most of it is often dissolved, but sample preparation must follow the laboratory's protocol.

use a bottle compatible with trace element analysis;
avoid cleaning products containing borax or boric acid;
comply with storage and acidification instructions;
indicate if the water is desalinated, brackish, groundwater, or from a well;
also measure sodium, chlorides, conductivity, and pH in case of salinization;
have any value near or above the applicable limit confirmed.

Borosilicate glass contains boron. Laboratories therefore use suitable containers, reagents, and analytical blanks to prevent sample contamination.

To evaluate a domestic treatment, collect the raw and treated water on the same day, after flow stabilization and in accordance with the laboratory's recommendations.

Which technologies can reduce boron in water?

Reverse osmosis

Reverse osmosis can reduce boron, but its efficiency strongly depends on pH, temperature, membrane type, pressure, recovery rate, and membrane condition.

At neutral pH, non-ionized boric acid passes through the membrane more easily. A single pass may therefore be insufficient to reach a very low concentration from water rich in boron.

Double-pass reverse osmosis

A second pass treats the permeate from the first. In desalination plants, it is often combined with pH adjustment to convert part of the boric acid into borate.

Boron-selective resins

Resins containing specific functional groups can capture boron with higher selectivity than conventional anionic resins. They require rigorous regeneration and effluent management.

Electrodialysis and electrodialysis reversal

These processes can reduce ionized species, but their effectiveness on uncharged boric acid at neutral pH is limited. pH adjustment may be necessary.

Nanofiltration

Nanofiltration is generally less effective than reverse osmosis for boric acid. Results are highly dependent on the membrane and operating conditions.

Adsorption

Certain aluminum, magnesium, and iron oxides, as well as functionalized materials, can adsorb boron. Performance is sensitive to pH and competing ions.

Conventional coagulation

Coagulation, sand filtration, and standard activated carbon are generally ineffective against dissolved boron at the concentrations encountered in drinking water.

Distillation

Distillation can reduce non-volatile boron, provided it is designed correctly and there is no droplet carryover.

Boiling

Boiling water does not remove boron. Since water evaporates while boron remains in the container, its concentration may even increase.

Adjusting the pH to a high level improves boron removal, but it should not be performed without professional design. The water must then be neutralized and stabilized before consumption.

How to evaluate the performance of a filter regarding boron?

Boron is one of the most difficult contaminants to reduce with standard domestic systems. A simple claim of "mineral" or "heavy metal" reduction does not constitute proof.

Element to check	Why is it important?
Boron explicitly mentioned	Boron's behavior differs from that of many salts and metals.
Influent concentration	Seawater, brackish water, and freshwater do not pose the same challenge.
Test pH	It determines the proportion of boric acid and borate ion.
Temperature	High temperature can reduce boron rejection by certain membranes.
Membrane type and age	Performance varies according to the technology and the device's condition.
Treated volume	A selective resin can become saturated before the end of the life of other media.
Final concentration	It must be compared to the applicable regulatory value.

The performance of a filtration system must be evaluated based on specific tests conducted by its manufacturer. In the absence of published results regarding this contaminant, no numerical reduction can be claimed.

For water naturally rich in boron, an analysis before and after treatment must be repeated periodically, especially after membrane replacement, flow rate changes, or pH adjustments.

View Monderma certifications and analyses

Frequently asked questions about boron in water

Is boron dangerous in water?

Excessive chronic exposure can have reproductive and developmental effects in toxicological studies. The risk depends on the concentration and duration of exposure.

What is the European limit?

The general parametric value is 1.5 mg/L. A value of 2.4 mg/L may apply in certain networks supplied primarily by desalinated water or in specific geological contexts.

What is the WHO value?

The WHO sets a guideline value of 2.4 mg/L.

Why is the Canadian value higher?

Health Canada sets 5 mg/L as the maximum acceptable concentration, taking into account treatment feasibility, while the calculated health-based value is higher.

Do the United States regulate boron?

There is no specific mandatory federal limit. The EPA issues a non-regulatory lifetime health advisory of 5 mg/L.

Can boron be detected by taste?

No. At health-based concentrations, it generally produces no characteristic taste, odor, or color.

Is boron common in seawater?

Yes. Seawater naturally contains several milligrams of boron per liter, mainly in the form of boric acid.

Can desalinated water still contain boron?

Yes. Boric acid passes through certain membranes more easily than highly charged ions. A second stage may be necessary.

Does boiling water remove boron?

No. On the contrary, boiling can concentrate boron as water evaporates.

Does a sediment filter remove boron?

No, except for a small fraction associated with particles. Boron is generally dissolved.

Does activated carbon remove boron?

Standard activated carbon is generally not an effective treatment for dissolved boric acid.

Is reverse osmosis effective?

It can reduce boron, but performance is highly variable. pH, temperature, membrane, and number of passes are determining factors.

Why does pH influence treatment?

At neutral pH, boron is mostly present as uncharged boric acid. At high pH, it becomes more ionized and easier to retain.

What analysis should I request?

Request total boron. In case of suspected saline intrusion, add sodium, chlorides, conductivity, and pH.

Is boron carcinogenic?

Available data do not lead to considering it an established carcinogen via ingestion. Health-based values are primarily based on reproductive and developmental effects.

Can boron damage plants?

Yes. It is essential in small doses but toxic to many crops when its concentration in irrigation water is too high.

Associated contaminants

Boron can be associated with salinity, geothermal waters, mineralized groundwater, and wastewater discharges.

Sodium Chlorides Sulfates Fluorides Arsenic Uranium Barium Nitrates

Scientific and administrative sources

This factsheet is based on public agencies, regulatory texts, and governmental scientific databases. No commercial blog or affiliate site is used as a primary health source.

World Health Organization – Boron
View the official WHO factsheet
WHO – Thematic page on boron
View the WHO thematic page
European Union – Directive (EU) 2020/2184
View the directive on EUR-Lex
Health Canada – Technical document on boron
View the Health Canada document
Environmental Protection Agency – Boron
View the EPA documents
EPA – Non-regulatory health-based levels
View the official EPA page
PubChem – Boron
View the PubChem factsheet
Monderma – Laboratory certifications and analyses
View Monderma certifications and analyses

Health warning: this factsheet is provided for informational purposes only. It does not replace an analysis performed by a laboratory, recommendations from the competent health authority, or the advice of a healthcare professional.