SOLARHEALTH

How to Read Your Swiss Tap Water Report Before Buying a Filter

A person reads a printed report beside a water glass and an open kettle with a pale ring inside.
The mark in the kettle is a reason to look up local water hardness. AI-generated illustration.

Key takeaways

  • Start with your address. A report is most useful when you know which supply zone serves your street and where the sample was taken.
  • Keep the less-than sign. In a real Swiss report, “<2 mg/L” and “40 mg/L” appear on the same nitrate line. They answer different questions.
  • Give limescale its own question. The hardness figure helps with the kettle and dishwasher. Lead and PFAS need their own tests.
  • If the concern starts at your tap, call the lab before filling a bottle. The time water has spent in the fittings can change a metals result.
  • Shop by the substance. Look for the exact cartridge and its certified reduction claim before committing to replacements.

The question at home: what would “better” water look like?

The white ring inside the kettle comes back a week after you clean it. Then someone at breakfast asks whether a filter jug would make the water better. It’s a fair question. Before you start comparing cartridges, ask what “better” would look like in your kitchen. Fewer flakes in the tea? A taste you prefer? An answer about the water that stood in the tap overnight? Each points you to a different line in the report or to a different place to take a sample. More background is in SolarHealth’s water guide.

Find the report for your street

Search for your municipality and Trinkwasserqualität, qualité de l’eau potable or qualità dell’acqua potabile. You can also enter your postcode or locality in the Swiss drinking-water directory. If the search draws a blank, ask your municipality which supplier serves your address. Swiss suppliers must give customers information about water quality at least once a year (drinking-water ordinance, Article 5; see also Canton Bern). Ask for the latest report for your supply zone. In a town with several sources, that extra detail matters.

Take Lenk in the Bernese Oberland. Its public notice dated 27 November 2025 names two springs and says the spring water undergoes UV treatment. There are separate entries for a reservoir, a spring intake and a fountain on the distribution network. Here’s what you can read from the three entries.

Where the water was sampledSample dateTotal hardnessNitrate
Rüti reservoir5 February 202523.8 °fH<2 mg/L
Blattibrunnen spring intake5 February 202513.2 °fH<2 mg/L
Waaghaus fountain, distribution network5 November 202519.3 °fH<2 mg/L

If you’re reading for a home in Lenk, the fountain is a useful place to start. It tells you something about water that had already travelled through the network. The figures beside the other place names help explain why a single hardness number for the whole municipality could be misleading. The February and November samples also came from different places, so reading down the column won’t tell you how hardness changed over the year.

What physics allows: a kettle, a litre and a less-than sign

Hardness describes the calcium and magnesium dissolved in water. Heating can make calcium carbonate come out of solution and settle on the kettle. The French degrees of hardness you’ll see in Swiss reports, written °fH, are useful when setting a dishwasher or choosing how often to descale (SVGW on limescale). A white kettle ring can therefore tell you something quite specific. If your question is about a trace substance such as lead, the hardness line leaves that question open.

Now look at the nitrate result. At the Waaghaus fountain, <2 mg/L means the amount was below the laboratory’s limit for reporting a numerical concentration. 40 mg/L is the Swiss maximum for nitrate (ordinance, Annex 2). Writing “2” in a notebook would turn a reporting limit into a measurement. Writing “zero” would claim more than the method could establish. Keep the little < when you copy the result.

Here’s a way to picture the scale. A 250 mL glass holds a quarter of a litre. At the concentration reported for that November sample, a glass would have contained less than half a milligram of nitrate. That’s concentration multiplied by volume. When another row uses micrograms per litre, remember that 1 mg equals 1,000 µg. Compare each substance with its own benchmark in matching units. The biggest number on the page needn’t be the one that answers your question.

The last few metres belong to your building

Water arriving at your building still has to pass through pipes, valves and a tap. While it sits there, small amounts of metal can enter it from some fittings. At ETH Zurich, investigators found elevated lead or nickel in some samples after water had stood in the plumbing. Follow-up samples taken after flushing met the requirements (ETH Zurich). That’s why a lab may want the first draw for one question and a flushed sample for another. The choice is part of the measurement. More in Lead and copper at the tap.

What tests show: where each claim stands

  • Supported: Lenk’s network sample contained nitrate below the laboratory’s 2 mg/L reporting limit on 5 November 2025 (municipal result).
  • Supported: Water left standing in some fittings can acquire lead or nickel, as the sampling investigation at ETH Zurich showed (investigation and follow-up).
  • Supported: An independently certified filter can reduce a named substance under defined test conditions when the listing covers that model, cartridge and claim (NSF certification guide).
  • Untested: Whether your jug lowers the concentration of a particular PFAS at your tap is an open question if all you have compared is taste or readings from a dissolved-solids pen (USGS on conductivity, PFAS laboratory methods).

What you can do anyway

Give one line in the report a closer look

Pick the question that sent you looking and copy the row that answers it. Keep the substance, result, unit, sampling point and date together. Add whether the figure is a single result, an annual average or a maximum. A yearly average is useful for describing the supply over time. If you want to know the highest result measured that year, ask for the range or maximum. If a result is above the applicable limit, ask the supplier what action it has taken and whether there’s advice for your address. A current drinking-water notice takes priority over the annual report (Canton Zurich, Canton Lucerne on current water incidents).

A missing row is often a reason to send an email before you buy anything. For PFAS, a family of chemicals, a useful question is “Which compounds did you analyse for my supply zone, when did you sample, and what was the reporting limit for each?” A blank space in a public summary could simply mean the detailed results sit in another document. If the supplier reports a sum, ask which compounds went into it. That gives you something you can compare with a lab or filter claim later (Swiss food safety office on PFAS; PFAS in tap water).

Decide whether your kitchen needs its own sample

If your concern is the first cold water drawn each morning from one particular tap, tell the lab exactly that. If you rent, share the question with the property manager, who can check which fittings are installed or were recently replaced. Ask a laboratory accredited for the substance in drinking water to supply its bottle and collection instructions (Swiss Accreditation Service directory; federal guidance on building plumbing). Tell it if there’s already a softener or filter, and where. Let the lab specify any standing time and whether you should flush. An empty jam jar filled before the phone call can leave the most important detail unknown.

A handheld pen labelled TDS, for total dissolved solids, is tempting because it gives an immediate number. Most such pens estimate dissolved solids from how readily water conducts electricity. Common dissolved ions contribute to the reading together. A change can be useful when checking a reverse-osmosis unit (NSF on reverse osmosis), but the pen cannot tell you how much lead or which PFAS are in a glass. If your decision depends on lead, put “lead in cold tap water” on the lab request. What changes after reverse osmosis is covered in remineralisation after reverse osmosis.

Take your question to the filter listing

For a chlorine taste, look for an explicit chlorine taste-and-odour reduction claim under NSF/ANSI 42. For lead, look for the words lead reduction against the exact model and cartridge. NSF/ANSI 53 covers specific contaminant claims. NSF/ANSI 58 covers reverse-osmosis systems, with separate claims for substances such as nitrate or lead. The numbers describe different tests. Open the certifier’s directory and check what your product actually passed (NSF standards guide; water filtration technologies explained).

You can practise with a real entry. The listing for the Whirlpool WHER25 names two replacement modules, WHEERF and WHEERM, and includes both lead reduction and nitrate/nitrite reduction. Someone asking about PFAS would still need to find a PFAS claim covering their target compounds. Before buying any model, check how many litres the cartridge is rated for, its operating flow and when the maker says to replace it (NSF on product labels). If the performance at your own tap matters, arrange comparable inlet and outlet samples with the lab.

And if it was the kettle that started all this? Put the local hardness figure beside the dishwasher manual, descale the kettle as its maker advises, and see whether that solves the nuisance. You can finish there. The next time a water question lands on the breakfast table, you’ll know where to find the row that matters.

Sources

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