Tap Water pH: What It Means and Does a Faucet Filter Change It?
The pH of tap water indicates whether it is acidic, neutral or alkaline on a scale from 0 to 14, and this information is publicly available for your own municipality, so you can look it up rather than guess. This figure is not the same as hardness, denoted TH, which measures only dissolved calcium and magnesium: water can be hard and still close to neutral, or soft with a pH that differs from neutral, because one of these measurements can never be used to infer the other. As for a faucet-mounted filter, such as the four-layer stainless steel model sold by Hydrion, its product page describes effects on taste, odours and limescale, not on pH: it makes no claim that it changes this value, and explicitly states that it does not reduce total dissolved solids (TDS).
- pH is measured on a scale from 0 to 14, with 7 marking neutrality; below 7, water is acidic, and above 7, it is alkaline.
- TH (hardness) and pH are separate measurements: the value of one can never be inferred from the other.
- The actual figure for your water is published by your municipality; it should not be estimated from the taste or feel of the water at the tap.
- A carbon/anti-scale filter affects taste, odours and limescale, but its product page makes no claim that it affects pH or total dissolved solids.
What pH measures, explained simply
pH expresses the balance between free hydrogen ions (H+) and hydroxide ions (OH-) present in water, on a scale from 0 to 14, with 7 marking neutrality (source: USGS Water Science School). Below 7, water contains relatively more H+ ions and is said to be acidic; above 7, it contains relatively more OH- ions and is said to be alkaline, or basic. This value says nothing about the amount of dissolved minerals in the water: two waters with the same pH can contain very different amounts of calcium, magnesium or other salts, and vice versa. That is why it is not possible to guess the pH of your tap water from its taste, clarity or the feeling of “hardness” often associated with limescale buildup in a kettle: these clues relate to a different measurement, not to pH itself.
pH and hardness (TH): why they are two different measurements
Water hardness, denoted TH in France for titre hydrotimétrique, measures only two specific ions: calcium and magnesium (source: Wikipedia, Titre hydrotimétrique). It is expressed in French degrees (°f), and this is the figure that explains the white deposit that forms in a kettle or on faucets over time. pH, on the other hand, measures a different ionic balance—that of hydrogen and hydroxide—which has no direct connection to the amount of calcium or magnesium present. Water can therefore be very hard, with a high TH, and still have a pH close to neutral, or be soft with a pH that differs from 7: trying to estimate one of these figures from the other, for example by reading the TH shown on a filter jug, leads to a false conclusion.
TH reference points, from very soft to very hard
To put a TH figure into context, the usual classification places water below 7°f in the “very soft” category, and water above 40°f in the “very hard” category, with intermediate levels in between (source: Wikipedia, Titre hydrotimétrique). These reference points are used to assess water’s tendency to form scale, that is, its ability to deposit limescale, and have no bearing on its acidity or alkalinity.
Where to find the actual pH of your tap water
The results of health inspections of tap water are public information, published for each municipality (source: Service-public.fr, Tap Water Quality). There are three ways to check the actual pH in your area: the annual water quality report included with your bill, which lists the parameters monitored throughout the year; your town hall, which makes the results available on request; and the municipality search tool published by the Ministry of Health, which provides access to analysis reports. The most useful thing to do is find the “pH” line in the document and read the value as shown, rather than assume a figure: it varies from one municipality to another and from one water source to another, and only an actual analysis of your area provides a reliable answer.
pH: a guide to everyday use, not just a health indicator
In guidelines such as the US Environmental Protection Agency’s (EPA) non-binding secondary standards, pH is monitored within a range of 6.5 to 8.5 as a guide to everyday use, not as a strict health limit (source: US EPA, Secondary Drinking Water Standards). A low pH is associated with a metallic taste and a tendency to corrode pipes, while a high pH is associated with a slippery feel and deposits. This guideline tracks pH separately from hardness and the recommended limit for total dissolved solids, which clearly illustrates why these three quantities—pH, TH and TDS—are published as three separate figures rather than combined into a single indicator.
Does a faucet-mounted filter change this figure?
Hydrion’s stainless steel faucet water filter product page describes four filtration stages: a coconut-shell carbon block for sediment, taste and odours; a silver-impregnated layer for antibacterial action; an anti-scale layer targeting hardness; and KDF media that the product page says targets chlorine and heavy metals. The stated filtered flow rate is up to 1.9 L/min.
Its product page makes no mention of any effect on pH, and explicitly states that the device does not reduce total dissolved solids, while preserving the minerals naturally present in the water.
An integrated diverter lets you switch between filtered and unfiltered water, so you can reserve the filtered setting for drinking and cooking water and thus preserve the cartridge’s lifespan. In practical terms, the honest answer is this: this filter is designed for taste, odours, perceived chlorine and limescale buildup, not for the pH figure you have just looked up in your municipality’s report. If that value concerns you for other reasons, it remains independent of what this device is designed to treat.
pH, TH and TDS side by side
The following table summarises the three quantities mentioned above and what the filter’s product page says about each, so you can compare them at a glance.
| Measurement | What it actually reflects | Typical unit or reference point | What the filter’s product page says |
|---|---|---|---|
| pH | Balance between hydrogen and hydroxide ions | Scale from 0 to 14, neutral at 7 | No effect on this value is claimed |
| TH (hardness) | Concentration of calcium and magnesium ions | French degrees (°f) | Anti-scale layer targets deposits related to limescale |
| TDS | Total dissolved solids, including minerals | Milligrams per litre (mg/L) | Explicitly not reduced, to preserve minerals |
Once you have found the actual pH and TH of your water in your municipality’s report, you can judge more precisely whether a filter like this meets your needs—whether that means a chlorinated taste, odours or limescale deposits on the tap—rather than a desire to change the pH itself. To learn more about total dissolved solids, the article on TDS, tester readings and common misconceptions about it explains what this figure measures and how to interpret it. If your question is more broadly about tap water quality in Europe, the overview of commonly tested contaminants puts pH in a wider context. And if you come across the unit GPD while comparing filtration systems, the explanation of GPD and the pure water/reject water ratio defines it in relation to the flow rate in litres per minute used here. You’ll find more practical guides on water chemistry on the Hydrion blog.