Contaminants in Tap Water: What Lab Tests Really Show

You turn on the tap, fill a glass, and drink. No second thought about what might have happened to the water on its way from the treatment plant to your kitchen. Or you reach for a bottle of mineral water, because the label says “natural” and “pure.” Either way, you’re trusting a promise you’ve never actually checked yourself.

That’s exactly what we did for our earthfilter—not with marketing claims, but with independent laboratory analyses. The Dr. Pötsch laboratory in Großwarasdorf (Austria) tested the filter between January and July 2026 for bacteria, parasites, microplastics, chlorine, heavy metals, and pharmaceutical residues. The test reports reveal two things at once: just how effective our filtration system can be—and just how wide the gap is between what is regulated by law and what actually ends up in the water.

This article summarises the test results – including the uncomfortable footnotes that sit in the lab reports but rarely get quoted.

Why “tested” water isn’t automatically free of contaminants

Germany’s drinking water regulation (Trinkwasserverordnung, TrinkwV) is rightly considered one of the strictest frameworks in Europe. The problem isn’t the limit values themselves – it’s where they’re measured, and where they aren’t.

Oversight ends at the water meter

Water utilities are responsible for water quality up to the handover point – usually the water meter. Everything that happens after that – in the pipes of your building, at old fittings, in water that’s sat in the line overnight – becomes the property owner’s responsibility, not the utility’s (source: Haufe, German).

From lab report 26/533/5M (translated)

“Copper in drinking water affects the largest part of the population, since copper pipes are installed in most homes […] Nickel doesn’t normally appear in drinking water. If nickel is found in your water sample, it most likely comes from the tap itself […] If too much chromium is found in your water sample, it most likely comes from the tap.”

These are exactly the metals – copper, nickel, chromium, zinc – your water utility never tests for, because they only appear after the water meter. Your official water quality report says nothing about them.

There’s no binding limit for pharmaceutical residues

This is the part that surprises most people: for pharmaceutical residues, hormones, and many antibiotics, there is no legal limit in Germany’s drinking water regulation. They simply aren’t part of the routine testing programme run by water utilities and health authorities. Germany’s Federal Environment Agency (Umweltbundesamt, German) only recommends a precautionary guidance value (GOW) of 0.1 µg/l per individual substance – a recommendation, not an obligation. 414 active substances have already been detected in the environment, and therefore potentially in drinking water too. Testing is mostly risk-based, for example in catchment areas with hospitals or intensive livestock farming.

From lab report 26/532/6M (translated)

“Due to the annual consumption of roughly 30,000 tonnes of pharmaceuticals in Germany alone […] these compounds are being found in increasing concentrations in water bodies […] they are often only inadequately removed by sewage treatment plants.”

Bottled water isn’t an automatic alternative

So if you switch entirely to bottled water, you’re trading one trust problem for another. A widely cited study by researchers at Columbia University and Rutgers University found an average of around 240,000 micro- and nanoplastic particles per litre in common mineral water brands sold in plastic bottles, with individual samples reaching up to 400,000. Independent Öko-Test analyses also found up to 500,000 particles per litre in individual single-use PET bottles – reusable bottles scored noticeably lower, but not zero. A label reading “pure from the source” says nothing about what gets added on the way through the bottling plant.

How the earthfilter is built: ceramic alone isn’t enough

The ceramic filter made of clay and colloidal silver – the central element of the earthfilter – handles mechanical and biological filtration: it retains everything larger than its pores – bacteria, parasites, sand, microplastics. That works reliably and with virtually no wear, because it’s a purely physical barrier.

Chlorine, dissolved heavy metals, and pharmaceutical residues, however, aren’t present in water as particles – they’re dissolved at the molecular level, far smaller than even the finest ceramic pore. No sieve, however fine, can hold them back. That’s exactly why we combine the ceramic filter with further filter materials: activated carbon binds chlorine and organic compounds such as pharmaceutical residues on its enormous internal surface area (adsorption), zeolite binds heavy-metal ions through ion exchange, and chlorine- and MPH/alkaline filter balls additionally help stabilise taste and pH.

That binding capacity is finite, though. Every grain of activated carbon or zeolite has a limited number of binding sites. Once they’re full, the material is saturated – it stops absorbing new contaminants and, in the worst case, can even release previously bound substances again. That’s why it’s best to replace the filter balls every three months: only then does the filtration performance measured in the lab stay consistent over time.

The earthfilter under independent lab testing: results at a glance

Seven lab reports, one goal: show what the earthfilter actually retains under lab conditions. The tests for chlorine, heavy metals, and pharmaceutical residues were carried out with the additional filter balls fitted; the tests for bacteria, parasites, and microplastics with the ceramic filter alone. We note which applies for each result.

1 · Bacteria: 100 % retention of E. coli

Lab report 26/527/2M dosed drinking water with Escherichia coli at three concentrations and ran it through the ceramic filter.

In all three cases, the filtrate was free of detectable E. coli bacteria – regardless of the original contamination level.

2 · Parasites, pollen, algae, cyanobacteria, and insects: consistently 100 %

Lab report 26/527/4M examined retention capacity based on the measured pore-size distribution (avg. 0.9 µm, maximum measured 1.2 µm, detection limit 0.1 µm, determined per ASTM F316).

The last row is worth noting: for very fine clay particles below 0.1 µm – smaller than the smallest pore measured – the lab acknowledges some residual permeability. That kind of transparency is exactly what makes the 100 % figures elsewhere credible.

3 · Microplastics: 99.99 % retention

Based on the same pore-size analysis (26/527/3M), the lab calculated the statistical retention rate for microplastic particles in the 1 to 5,000 µm range – the range covered by the German Federal Environment Agency’s definition. For context: that’s the same size range in which the particles found in bottled mineral water fall.

4 · Chlorine: over 99 % reduction

For the test with the additional filter balls (26/531/7M), 1 litre of tap water was dosed with a chlorine standard solution.

For context, from the lab report: the permitted limit for free chlorine at the tap is a maximum of 0.3 mg/l in Germany and Austria; the WHO cites a guideline value of up to 5 mg/l, and the US EPA 4 mg/l. Chlorine becomes noticeable to taste from around 0.6 mg/l.

5 · Pharmaceutical residues: 80–99.75 % reduction

This is where it gets particularly relevant – because, as described above, there’s no legal limit for this group of substances at all. For the test (26/532/6M), 1 litre of tap water was dosed with a standard solution (1 µg/L per substance).

From lab report 26/532/6M (translated)

“Carbamazepine is used to treat epilepsy. Because sewage treatment plants remove it only poorly or not at all, it is frequently detected in treatment-plant effluent and rivers […] Ibuprofen is among the most commonly detected pharmaceutical residues in water bodies worldwide […] Residues are regularly found in wastewater, rivers, lakes, sewage sludge, and in groundwater or drinking water.”

6 · Heavy metals: 87–99.9 % reduction

Here, too, 1 litre of tap water was dosed with a heavy-metal standard solution and passed through the earthfilter fitted with further filter materials (26/533/5M).

Notably, exactly the metals that, according to the lab’s notes, typically originate in a building’s own plumbing – copper, nickel, chromium, zinc – are reliably removed here. That closes the gap that official water testing structurally leaves open.

7 · Material safety: the filter itself doesn’t release anything harmful

A good filter is useless if it becomes a source of contamination itself. That’s why the ceramic material was tested for lead and cadmium leaching under EC Regulation 1935/2004 (food-contact materials) (26/527/1M):

Both values are far below the limits set by the EU regulation for ceramic articles intended for food contact.

Tap water, bottled water, or a water filter: an honest comparison

The point isn’t to demonise tap water – German and Austrian tap water is, by international standards, among the most tightly controlled anywhere. The point is: oversight up to the water meter isn’t the same as oversight up to the glass in your hand. And a label that says “natural” doesn’t replace a lab report.

What this means for you

• Blind trust is the real risk factor. Neither “the state already checks that” nor “bottled water is naturally pure” holds up to closer scrutiny – for different, but equally real, reasons.
• The last few metres matter. Most of the heavy metals found in drinking water don’t come from the treatment plant – they come from a building’s own plumbing, exactly where official oversight ends.
• Entire categories of contaminants still aren’t regulated at all. Pharmaceutical residues are the clearest example: 414 detected active substances in the environment, but no binding drinking-water limit.

Filtering right at the point of use – with results you can independently verify – closes exactly that gap, regardless of how well the water utility or the bottled water source actually performs.

Limits of this study

For context, so you can weigh the results appropriately:

• The pore-size measurement itself notes that other areas of the same filter may show different values – the results apply to the specific unit tested, “earthfilter No. 21.”
• The lab reports were commissioned by earthfilter GmbH. That’s standard practice in the industry (regulatory approval processes work the same way), but it should be stated transparently.
• The tests reflect controlled, dosed lab conditions, not long-term field measurements across a filter cartridge’s full service life.

 

Conclusion: trust is good, a lab report is better

The seven lab reports from Labor Dr. Pötsch show a ceramic water filter that, under lab conditions, reduces E. coli to 0 CFU/100 ml, fully retains parasites and microorganisms, filters out 99.9998 % of the microplastics tested, removes over 99 % of chlorine, reduces 80–99.75 % of selected pharmaceutical residues and 87–99.9 % of selected heavy metals – and doesn’t release lead or cadmium in any health-relevant amount itself.

Just as important as these figures is what’s in the notes of the lab reports: neither official drinking-water oversight nor the bottled-water aisle automatically covers everything that can end up in your glass. If you’d rather not leave that to chance, filter your water where it’s actually drunk – right at your own tap.

Sources: Lab reports, Labor Dr. Pötsch 26/527/1M–4M, 26/531/7M, 26/532/6M, 26/533/5M · Umweltbundesamt (German) · Öko-Test (German) · Columbia University / Rutgers University (via Overton Magazin, German) · Haufe (German)