Nickel in drinking water: limit value, causes and symptoms

Nickel is a silvery-white metal with the atomic number 28. It is one of the heavy metals. In its pure form, nickel is insoluble in water. Industry mostly processes the metal as a nickel alloy. Particles from these alloys are released into drinking water.

Nickel is best known as a trigger of contact dermatitis (contact eczema of the skin). The heavy metal causes one of the most common contact allergies worldwide. The European Centre for Allergy Research Foundation (ECARF) evaluated data from more than 100,000 patients between 2005 and 2014. 15.5% of adults in Germany showed nickel sensitisation. This means that around 1 in 7 Germans react to the metal. Women are affected significantly more often than men.

Because it is so common, the EU has restricted the use of nickel since 1994 through the EU Nickel Directive (Directive 94/27/EC). Today, the REACH Regulation (EC) No 1907/2006 governs the nickel content of goods that come into direct contact with the skin. REACH stands for Registration, Evaluation, Authorisation and Restriction of Chemicals. The regulation covers these products: jewellery, watches, buttons, rivets and fasteners. For drinking water, on the other hand, only the Drinking Water Ordinance applies.

Nickel alloys resist corrosion and withstand high temperatures. That is why they are found in industrial plants, in stainless steel and in everyday appliances. Nickel is therefore one of several heavy metals in tap water. These also include lead, copper and cadmium.

Nickel gets into drinking water in two ways. Part of it comes from groundwater. The sources there are fertilisers containing nickel or industrial wastewater. The larger share is released by fittings, taps and pipes in the house. The last mile is the route the water takes from the house connection to the tap. The most common cause of nickel in drinking water is therefore found in your own home.

Waterworks intercept the contamination from groundwater. They treat the water and take regular measurements before it is delivered to the end consumer. Values above the limit value do occur, for example in the event of malfunctions at the waterworks. However, they remain the exception.

The limit value for nickel in drinking water is 0.02 milligrams per litre. It applies in Germany and in all other EU countries. Any value above 0.02 mg/l means too much nickel in drinking water. The 2023 amendment to the Drinking Water Ordinance leaves this value unchanged.

The Drinking Water Ordinance regulates heavy metals individually. A comparison with 3 other heavy metals shows how strictly nickel is classified:

In its Guidelines for Drinking-water Quality, the World Health Organization (WHO) gives a guideline value of 0.07 mg of nickel per litre. At 0.02 mg per litre, the European limit value is around 3 times lower than the WHO recommendation.

Waterworks monitor nickel levels as part of their legal obligation to take samples. If a sample exceeds the limit value, the water supplier takes immediate action. It then reduces the pollutant content. The 2023 amendment to the Drinking Water Ordinance tightens the sampling requirements. It also lowers individual limit values, for example for lead and legionella.

Nickel is toxic, but only in high doses. The body absorbs nickel poorly via the intestine. It excretes small amounts again without processing them. With water at the limit value of 0.02 mg per litre, poisoning does not occur. Here, too, the dose makes the poison.

The European Food Safety Authority (EFSA) has derived a tolerable daily intake (TDI) for nickel. It is 13 micrograms per kilogram of body weight per day. For an adult weighing 70 kilograms, this corresponds to around 0.91 mg of nickel per day.

A calculation using the legal maximum value puts this into perspective. Anyone who drinks 2 litres of water containing exactly 0.02 mg of nickel per litre takes in 0.04 mg of nickel. That is about 4% of the tolerable daily intake of an adult weighing 70 kilograms. Drinking water therefore remains a minor source of nickel. What becomes critical is the total from all sources, especially from foods containing nickel.

Nickel is a carcinogen, i.e. a cancer-causing substance. The classification covers the heavy metal and its compounds. The risk mainly concerns the respiratory route. If nickel is inhaled as fine particulate matter, the heavy metal is particularly dangerous.

Those primarily affected are people who handle nickel dust at work. For oral intake via food or drinking water, on the other hand, a carcinogenic effect has not yet been confirmed. A glass of tap water and a shift in metalworking are two routes of intake with two different risks. The Umweltbundesamt lists nickel in fine particulate matter as a separate air quality parameter.

Too much nickel in drinking water mainly manifests itself in the gastrointestinal tract. Typical symptoms are nausea and vomiting. They occur when the amount of nickel significantly exceeds the tolerable daily intake of 13 micrograms per kilogram. This is unlikely from tap water alone.

The long-term consequences of a permanently excessive nickel intake are unclear. Children bear the higher risk. For its risk assessment, EFSA evaluated more than 47,000 measurements. Among infants, toddlers and children, the most highly exposed 5% exceed the tolerable daily intake through their overall diet. In adolescents and adults, intake remains below it. The report also cites evidence from rodent studies: organ damage and neurological deficits after a long-term increased nickel dose. So far, there is insufficient evidence of the same effect in humans.

One group deserves particular attention: people with a nickel allergy react even to amounts that are unproblematic for others.

Drinking water is one of several sources of nickel in everyday life, alongside food and everyday objects. People with a nickel allergy therefore also react to nickel that they drink or eat. In some cases, oral intake influences the frequency and severity of nickel contact dermatitis.

A nickel allergy always begins with sensitisation. The first contact with the allergen only produces the preliminary stage of the allergy. Only renewed contact triggers the allergy. A dermatologist confirms the diagnosis with an epicutaneous test (patch test on the skin).

According to the review on systemic nickel allergy syndrome (SNAS), the symptoms of an oral nickel allergy include the following:

• skin reactions such as pustules or eczema
• gastrointestinal reactions such as nausea and abdominal pain
• fever

For people who are already sensitised, EFSA cites a reference value of 4.3 micrograms of nickel per kilogram of body weight. This is the lowest single dose at which eczematous skin reactions occurred in studies. Experts call this systemic contact dermatitis. This value is not a safety threshold: sensitive individuals react even below it. EFSA therefore applies a safety margin to this reference value.

For drinking water, the assessment is favourable. EFSA classifies a glass of tap water on an empty stomach as harmless to health. The situation is different for the diet as a whole: EFSA assesses the short-term nickel intake from all foods combined as a concern for people with a nickel allergy. Tap water is therefore not the main source. However, it is the share that is easiest to reduce.

According to the Umweltbundesamt, an allergic reaction to orally ingested nickel only occurs from a relatively high dose. That is precisely why the limit value for drinking water is set so low:

> The guideline value of 0.02 mg of nickel per litre of drinking water is intended to ensure that only 10% of the amount of nickel taken in daily with food is ingested via drinking water.

Foods containing nickel push daily intake up even further. The Bundesinstitut für Risikobewertung (BfR, German Federal Institute for Risk Assessment) has estimated long-term nickel intake from food. This was based on its study of typical meals. A low-nickel diet nevertheless remains a matter for medical advice, as it requires a major change in eating habits. Filtering the water is the simpler lever.

3 measures reduce the nickel content of tap water: letting stagnant water run off, replacing taps and installing a water filter. Beforehand, a drinking water analysis provides clarity about the actual level.

A certified laboratory tests a water sample for nickel. In the same run, it checks for other contaminants, such as other heavy metals and bacteria in tap water. The results allow you to plan the next steps instead of acting on suspicion.

If the results confirm an elevated level, these measures help:

• Let stagnant water run off. Run the water briefly before use. The first portion from the pipe is the one most heavily contaminated with nickel.
• Check taps and pipes. Check whether the taps are chrome-plated and, if possible, replace them with nickel-free alternatives.
• Install a water filter. A filter works directly at the tap, i.e. downstream of the last mile.

A water filter is the practical solution if the cause lies in the pipes and taps. Replacing them usually means costly construction work.

A common misconception concerns boiling: boiling does not remove nickel from drinking water. Heat kills bacteria. Heavy metals such as nickel remain in the water. As the water evaporates, they even become slightly more concentrated.

An activated carbon block filter binds heavy metals such as nickel directly at the tap. The filter works exactly where the nickel gets into the water: downstream of the domestic plumbing. For people with a nickel allergy, this is the simplest lever. Taps and pipes can only be replaced with construction work.

The filtering effect is based on adsorption. Pollutants adhere to the porous surface of the carbon. Minerals and trace elements remain in the water. How this material is structured is explained in the guide What is activated carbon. The differences between the designs are described in the article on activated carbon filters for water.

For household use, a solid block filter is better suited than loose granules. The ACTIVE+ filter cartridge from Alb Filter works with sintered activated carbon. In addition to heavy metals, it also binds chlorine and organic residues. An overview of all variants can be found under water filter cartridges. For connection to the kitchen tap, see the page on the drinking water filter.

Jug filters are the weaker choice for this purpose. They mainly improve taste and odour. Standing water in the container also brings a risk of germ growth in jug filters. A reverse osmosis system also removes heavy metals. However, it also removes minerals from the water and requires considerably more equipment under the sink.