Nitrates in Drinking Water: UK Limits and How to Remove Them

Nitrate contamination is a common concern for properties supplied by private boreholes, wells and springs, particularly in agricultural areas.

Although nitrate occurs naturally in the environment, elevated concentrations in drinking water can pose health risks. Fortunately, effective treatment methods are available, including nitrate-selective ion exchange systems and reverse osmosis.

In this guide, we explain the UK drinking water limit for nitrate, how to interpret your water analysis and how ion exchange treatment can reduce nitrate concentrations.

What Are Nitrates and Where Do They Come From?

Nitrate (NO₃⁻) is a naturally occurring compound containing nitrogen and oxygen. It is highly soluble in water and can travel through soil into underground water sources.

Common sources of elevated nitrate include:

Agricultural fertilisers: Nitrates from fertilisers can be washed into groundwater following rainfall.
Animal manure and slurry: Agricultural waste can contribute to nitrate contamination.
Septic tanks and wastewater: Poorly maintained drainage systems may contribute to groundwater pollution.
Natural decomposition: Organic material releases nitrogen compounds that can eventually form nitrate.

Boreholes and shallow wells in agricultural areas can be particularly vulnerable, although nitrate levels can vary considerably between locations.

What Is the UK Legal Limit for Nitrate in Drinking Water?

The UK drinking water standard for nitrate is 50 mg/L, measured as nitrate (NO₃⁻).

This applies to public drinking water supplies and is also the prescribed standard for private drinking water supplies.

Understanding Nitrate and Nitrate-Nitrogen Results

Water analysis reports do not always express nitrate concentrations in the same way.

Some laboratories report nitrate as NO₃⁻, while others report nitrate-nitrogen (NO₃-N).

These are two different ways of expressing the concentration of the same substance.

Measurement	Equivalent concentration
Nitrate (NO₃⁻)	50 mg/L
Nitrate-nitrogen (NO₃-N)	11.3 mg/L
Nitrate-nitrogen (NO₃-N)	10 mg/L
Equivalent nitrate (NO₃⁻)	44.3 mg/L

To convert nitrate-nitrogen to nitrate:

Nitrate (mg/L as NO₃⁻) = Nitrate-nitrogen (mg/L as N) × 4.43

For example, a laboratory result of 12 mg/L nitrate-nitrogen is equivalent to approximately 53.1 mg/L nitrate, exceeding the UK drinking water standard.

Always check which units your laboratory has used before interpreting the results or sizing a treatment system.

Nitrite (NO₂⁻) is a separate parameter with its own drinking water standard. Where nitrate and nitrite are both present, the combined regulatory requirement must also be considered.

Why Are High Nitrate Levels a Concern?

The principal acute health concern associated with high nitrate concentrations is methaemoglobinaemia, sometimes called blue baby syndrome.

This condition can affect very young infants, particularly those under six months, because nitrate can be converted into nitrite in the digestive system, reducing the blood's ability to transport oxygen.

The UK Drinking Water Inspectorate also advises against regular consumption of water containing nitrate above 50 mg/L for adults.

If a private drinking water supply exceeds this level, a suitable alternative source of drinking water should be used while the situation is investigated and appropriate treatment arranged. This is especially important when preparing infant formula.

Boiling water does not remove nitrate. Prolonged boiling can actually increase its concentration as water evaporates.

How Can Nitrates Be Removed from Water?

Two established methods are commonly used for nitrate reduction:

Nitrate-selective ion exchange.
Reverse osmosis.

The most suitable approach depends on the nitrate concentration, other water chemistry, required flow rate and whether treatment is needed for the whole property or only drinking water.

Nitrate Removal Using Ion Exchange

Ion exchange is an established method for reducing nitrate concentrations in drinking water.

Unlike a conventional water softener, which uses cation exchange resin to remove calcium and magnesium, a nitrate reduction system uses a specialist anion exchange resin.

How Does Nitrate-Selective Resin Work?

The resin initially contains chloride ions.

As water flows through the resin bed, nitrate ions are attracted to the resin and exchanged for chloride ions.

This reduces the nitrate concentration in the treated water.

Over time, the resin's available capacity becomes exhausted and it must be regenerated to restore its ability to remove nitrate.

How Is the Resin Regenerated?

Nitrate reduction systems typically use sodium chloride (salt) for regeneration, in a similar way to conventional water softeners.

During regeneration:

A concentrated brine solution passes through the resin.
The brine displaces accumulated nitrate ions.
The nitrate-rich waste solution is discharged to a suitable drain.
The resin is rinsed before returning to service.

The regeneration process restores the resin's capacity to remove nitrate.

Correct regeneration settings are essential because nitrate can pass through the resin once its available capacity has been exhausted.

Why Use Nitrate-Selective Resin?

Not all anion exchange resins perform equally well when removing nitrate.

Conventional strong base anion resins can preferentially remove sulphate, reducing the available capacity for nitrate.

This can be particularly problematic where the water contains both elevated nitrate and sulphate.

Nitrate-selective resins are designed to favour nitrate removal, making them a better choice for many drinking water applications.

However, sulphate and other dissolved ions can still affect performance, so the complete water analysis must be considered when sizing the system.

GAPS Water Treatment supplies specialist nitrate-selective media, including PA202 Nitrate-Selective Ion Exchange Resin.

Choosing the Correct Nitrate Reduction System

A nitrate reduction system must be sized for the actual water chemistry and consumption.

Important considerations include:

Nitrate concentration: Higher nitrate levels generally reduce the volume of water that can be treated between regenerations.
Sulphate concentration: Competing ions can affect resin capacity and operating costs.
Daily water consumption: Determines the volume of water requiring treatment.
Service flow rate: The resin bed must be large enough to treat water effectively at the required flow.
Regeneration frequency: Must be sufficient to prevent nitrate breakthrough.
Other contaminants: Iron, suspended solids and organic contamination may require additional treatment.

Nitrate concentrations in private water supplies can also vary over time, particularly following seasonal changes and rainfall.

For this reason, regeneration settings should incorporate a suitable safety margin, and treated water should be tested regularly.

Clack-Controlled Nitrate Reduction Systems

GAPS Water Treatment supplies nitrate reduction systems incorporating Clack automatic control valves.

These systems are available in a range of vessel sizes and flow capacities to accommodate domestic, commercial and larger water treatment applications.

The control valve manages the regeneration cycle, while the nitrate-selective resin performs the actual nitrate removal.

View our Nitrate Reduction Systems

Can Reverse Osmosis Remove Nitrates?

Yes. Reverse osmosis (RO) is another effective method of reducing nitrate concentrations.

Reverse osmosis uses a semi-permeable membrane to reject a range of dissolved contaminants, including nitrate.

It can be particularly suitable for point-of-use drinking water treatment, where a relatively small quantity of treated water is required.

Ion Exchange vs Reverse Osmosis

Feature	Nitrate Ion Exchange	Reverse Osmosis
Main treatment method	Nitrate-selective resin	Membrane separation
Typical application	Whole-property or larger systems	Under-sink drinking water
Regeneration	Salt regeneration	Not normally applicable
Wastewater	Produced during regeneration	Produced during operation
Other dissolved contaminants	Primarily targeted anions	Reduces a broad range
Maintenance	Salt, resin and valve maintenance	Prefilters and membrane maintenance

For a property requiring nitrate reduction throughout the water supply, an appropriately designed ion exchange system may be more practical.

Where only drinking and cooking water needs treatment, a suitably specified reverse osmosis system may offer a more economical solution.

How Do You Know Whether Your Nitrate Filter Is Working?

Nitrate reduction systems require ongoing monitoring.

Unlike contaminants that cause staining, odour or discolouration, nitrate is generally invisible and has no distinctive taste.

This means that a system can become exhausted without any obvious change in the appearance of the water.

We recommend:

Testing the untreated water to establish nitrate concentrations.
Testing the treated water after installation and commissioning.
Checking performance regularly using a suitable nitrate test or accredited laboratory analysis.
Ensuring regeneration settings are appropriate for the measured nitrate concentration and water consumption.
Maintaining the system in accordance with the manufacturer's recommendations.

A conductivity or TDS reading alone cannot reliably confirm nitrate removal.

A nitrate reduction system should not be assumed to produce compliant drinking water without verification through testing.

Frequently Asked Questions

Will a normal water softener remove nitrates?

No. Conventional water softeners use cation exchange resin designed to remove hardness minerals such as calcium and magnesium. Nitrate removal requires an appropriate anion exchange resin or another suitable treatment method.

Will a sediment or carbon filter remove nitrate?

Standard sediment cartridges and conventional activated carbon filters are not effective methods of removing dissolved nitrate.

Will a UV system remove nitrates?

No. UV systems are used for microbiological disinfection and do not remove dissolved nitrate.

A private water supply may require both nitrate reduction and separate microbiological treatment if bacterial contamination is present.

How long does nitrate resin last?

The resin can be regenerated repeatedly, but its useful service life depends on water quality, operating conditions and maintenance.

The volume of water treated between regenerations depends on the nitrate concentration, competing ions, resin quantity and system design.

Is nitrate reduction suitable for borehole water?

Yes. Nitrate-selective ion exchange is widely used for nitrate reduction in groundwater and private water supplies.

However, a full water analysis is recommended to identify any additional treatment requirements.

Nitrate Reduction Systems from GAPS Water Treatment

At GAPS Water Treatment, we supply nitrate-selective ion exchange resins and complete nitrate reduction systems for domestic, commercial and industrial applications.

Whether you require a small drinking water treatment unit or a larger automatic nitrate reduction system, selecting the correct equipment begins with understanding your water quality.

Browse our Nitrate Reduction Systems

For assistance selecting a system, email your water analysis, required flow rate and estimated daily consumption to sales@gapswater.co.uk.

We can help you identify suitable equipment and provide a quotation.

GAPS Water Treatment supplies equipment and technical product advice. We do not provide on-site installation services.

Nitrates in Water and Their Removal Using Ion Exchange Systems