What are we drinking, exactly?

A water analysis fits on one or two pages. Parameter names, measured values, reference thresholds — and, at the very bottom, a conclusion. The document is imposing at first glance, then lets itself be read as soon as you know where to look. That is the point of this article.

Let us first be clear about what the report describes: your water, at your tap, on the day of sampling. Not the water of the next town, not a national average. Water changes with the source, the season and the pipes it crosses. So the reading starts with this simple truth: you are reading a snapshot, not a definitive portrait.

Where your tap water comes from

Depending on where you live, drinking water comes from springs, groundwater or lakes, in proportions that vary greatly from one region to another. In Switzerland, where the house was founded, it is captured, sometimes treated — often very lightly, so good is the resource — then distributed under control to the meter, and it counts among the most closely monitored foodstuffs in the country. Most utilities, there and elsewhere, publish their results.

Past the meter, however, the water runs through the building’s own installations: the last kilometre, the one nobody but you is responsible for. An analysis sampled at the tap tells the whole journey — public network and private installation included. That is what makes it more telling than a network average, wherever you live.

The three families of results

Whatever the laboratory, a report is organised around three families. Each answers a different question.

• The minerals — calcium, magnesium, sodium, potassium. They come from the rocks the water has crossed, and they sign its taste and its hardness.
• The residues — nitrates, metallic traces — sometimes from the indoor pipework —, remnants of treatment. They tell the story of the water’s journey to you.
• The comfort parameters — free chlorine, pH, turbidity, conductivity. They describe the balance of the water and how it feels in the glass.

None of these families is “good” or “bad” in itself. A highly mineralised water can be excellent; a very soft water too. What matters is knowing what you are drinking — and then deciding, according to your uses and your taste.

Four units to tame

The units do most of the intimidating. There are only four to know in order to read the whole document.

• mg/L — the milligram per litre: one thousandth of a gram dissolved in a litre of water — the same thing as one ppm. Most parameters are expressed this way.
• µS/cm — the microsiemens per centimetre measures electrical conductivity. The more dissolved minerals a water carries, the better it conducts current: a single, global figure for mineralisation.
• °fH — the French degree measures hardness — the calcium and magnesium content. One degree corresponds to 10 mg/L (10 ppm) of calcium-carbonate equivalent; some countries state the same value directly in ppm CaCO₃.
• pH — the balance between acidity and alkalinity, 7 being the neutral point. Mains water generally sits between 6.8 and 8.2 [to be confirmed — reference range].

What a TDS tester measures — and what it does not say

Little pocket “TDS” testers have spread through kitchens. TDS stands for total dissolved solids: the device actually measures the water’s conductivity, then converts it into an estimate of the total mass of dissolved matter, expressed in mg/L.

It is therefore a trend indicator, not an identification. The figure adds up everything that conducts current — calcium as much as sodium — without distinguishing anything. A renowned mineral water shows a high TDS; a very pure water shows a low one. In between, the figure alone says nothing of composition, taste or compliance. It takes on meaning in comparison: before and after a piece of equipment, or from one tap to another.

A real reading goes through the laboratory, parameter by parameter — TDS appears there, put back in context. The house’s analysis kit follows exactly that path.

Reading “compliant” like a technician

There remains the report’s conclusion: “compliant”. It means that every measured parameter respects the maximum values set by food law. That is good news, and it should be read for what it is: a legal threshold, designed for public health.

Beyond the threshold begins the domain of personal standards: the hardness that suits your coffee machine, the minerality that suits your palate, the finesse you expect in the glass. That is a choice, not a worry.

Drinkable is a threshold. Perfect is a standard.

A technician therefore reads a report in three moves: place the families, convert the units, compare with the thresholds. Then they ask the only question left: what do you want to do with this water? The answer belongs to you.