Silver ions in the water tank: what a silver mesh can and cannot do

In the camping trade, silver meshes are marketed with the promise of germ-free water for 6 months. The most frequent question about them concerns health. The answer to the health question is short and leads on to the question of how well they work.

There are 4 common types on the market, all of which work on the same principle. They differ in surface area and handling, not in the active substance.

• Silver mesh. A textile fabric with silver-plated threads that lies in the fresh water tank. It is sold in sizes graded by tank volume, with manufacturers usually stating a service life of 6 months.
• Silver pad. A flat mat made of the same material, intended for tanks without a large inspection opening.
• Silver ball. A spherical element made of silver or with a silver coating that lies loose in the tank.
• Silver sponge. A porous body with a larger surface area than a mesh of the same mass.

All 4 release silver in an uncontrolled way. The amount released depends on water temperature, pH value, chloride content and the age of the product. To date, the industry has published a release rate in mg per litre per day for 0 products. Only such a figure would make the concentration in the tank calculable and verifiable.

In 2018, the WHO evaluated the available studies on silver as a drinking water disinfectant. The figures from 3 of the studies evaluated show what this is about.

2 things stand out. First, silver takes hours to days. Second, the effective concentrations are 80 to 100 µg/l, i.e. 0.08 to 0.1 mg/l. The WHO considers 0.1 mg/l tolerable from a health perspective, and the former German maximum of 0.08 mg/l was even lower.

In other words, the concentrations at which silver had a measurable effect in the studies coincide with the values regarded as the upper limit. That leaves 0 safety margin between the effective threshold and the upper limit.

Its spectrum of action is also narrow. Of the 3 classes of pathogens, according to the WHO evaluation silver essentially only covers bacteria, with reductions of between 1.6 and 7.6 log10. For viruses and protozoa, the data are still too thin. The WHO minimum requirement for household devices calls for effectiveness against 2 of 3 pathogen classes, so silver does not clear this hurdle. 2 silver-containing products failed in the WHO evaluation scheme.

1 result from the same evaluation weighs more heavily for a motorhome tank than all the kill rates. In 2008, Silvestry-Rodriguez and colleagues tested whether 100 µg/l of silver prevents the formation of biofilm in the distribution system. The result: silver was ineffective, and there was no difference from the untreated control.

Biofilm is the coating that forms on tank walls, in hoses and on seals. A layer of slime shields the germs living in it. An agent that only treats the free water does not reach this coating.

A silver mesh therefore acts on the free water and leaves the coating on the wall untouched. If you change the mesh after 6 months and never clean the tank, you have an overgrown tank with silver-treated water.

On the same topic from a household perspective: Bacteria in tap water.

Silver is not on this list. The version in force is the notice published in the Bundesanzeiger (Federal Gazette) dated 13 January 2023 (BAnz AT 27.01.2023 B12), with a correction dated 17 July 2024, most recently confirmed on the Umweltbundesamt (German Environment Agency) website on 14 January 2026. A full-text check of all 27 pages returns 0 hits for silver. The only matches concern mercury (Quecksilber in German) as a purity requirement for other substances.

All 5 sections of the list were checked:

• Part I a lists treatment substances in the form of solutions and gases, such as flocculants.
• Part I b lists solids such as filter media.
• Part I c lists substances for disinfection, headed by calcium hypochlorite.
• Part II lists 10 disinfection methods, from chlorine dioxide dosing to irradiation with ultraviolet (UV) light in the 240 to 290 nm range.
• Part III lists substances for the Bundeswehr (German armed forces), a state of defence and disaster situations.

Part III is the most revealing. It contains the agents for emergencies, when the water supply is seriously at risk. Listed there are calcium hypochlorite and sodium dichloroisocyanurate, i.e. chlorine compounds. Silver is missing there too.

The introduction to the list also makes clear that its scope corresponds to that of the Drinking Water Ordinance. Since the amendment, the Umweltbundesamt has been responsible for the list, no longer the Bundesministerium für Gesundheit (Federal Ministry of Health).

Historically, things were different. In 2009, the Bundesinstitut für Risikobewertung (BfR, German Federal Institute for Risk Assessment) cited a permitted maximum of 0.08 mg/l for silver used to preserve stored water in small systems. In 2018, the WHO still listed 0.08 mg/l as the German regulation. Silver no longer appears in the ordinance in force today or in the list.

Alongside the Drinking Water Ordinance, the EU Biocidal Products Regulation (EU) No 528/2012 applies. It governs which active substances may be used in biocidal products at all, divided into 22 product types. Drinking water disinfection is product type 5.

With Implementing Decision 2014/227/EU of 24 April 2014, the Commission did not approve silver chloride for product types 3, 4, 5 and 13. The reasoning in the decision is remarkable: the participants had ended their participation in the review programme or had not submitted complete documentation.

What was established was therefore not harmfulness but non-approval for lack of evidence. Anyone who wanted to keep silver chloride on the market would have had to prove its effectiveness and safety, and chose not to.

Elemental silver must be distinguished from this. Delegated Regulation (EU) No 1062/2014 lists it in its review programme under number 401, including for product type 5. The evaluating Member State is Sweden. The 2014 non-approval expressly concerns silver chloride, not the metal itself.

Argyria is the best-documented consequence of excessive silver intake in humans. It manifests as an irreversible grey-blue discolouration of the skin and mucous membranes and is considered cosmetic rather than damaging to organs. Other effects are not described to any significant extent in the available human studies.

The WHO derived its 10-gram amount in 1993 from epidemiological and pharmacokinetic data and has not revised it since. The technical term for this is No Observed Adverse Effect Level (NOAEL), i.e. the highest dose with no observed adverse effect. To this day, there is no health-based guideline value for silver in the WHO guidelines, because data on its toxicity in humans remain thin.

The value of 0.1 mg/l is the subject of a confusion that runs through almost all guides. According to the WHO's explicit statement, it is a health advisory and not a guideline value. The WHO notes that the distinction between an advisory and a guideline value is rarely appreciated. The value, it says, is often wrongly cited as a limit value or permitted amount.

The Bundesinstitut für Risikobewertung (BfR, German Federal Institute for Risk Assessment) assesses nanosilver separately. In 2009, it recommended that manufacturers avoid nanoscale silver in food and everyday products until a conclusive risk assessment is possible. The same statement considers the use of silver as a surface biocide to be unnecessary, because it provides no benefit beyond the usual hygiene measures.

According to the manufacturer, products such as Micropur Forte combine 2 active substances: chlorine for rapid killing and silver for subsequent preservation. The division of tasks between the two substances explains why silver plays a role in such products.

Chlorine is listed as a disinfectant in Part I c and Part II of the list and, unlike silver, is approved for drinking water disinfection. However, it is used up over time and does not protect for weeks. Silver works slowly but stays in the water. In combination, each substance takes on the task it is suited to.

The legal finding nevertheless remains the same. Sodium dichloroisocyanurate is listed in Part III of the Umweltbundesamt list with a maximum permitted addition of 26 mg/l of free chlorine. The silver content of such tablets is not listed there.

What chlorine does in drinking water and where its limits lie is explained in Chlorine in drinking water.

Water preservation is the industry term for everything intended to keep water in the tank fresh. Without chemicals, this works via 6 steps, all of which tackle the cause rather than the symptom.