Filtered water with minerals

What is behind it

The data basis is unusually broad. The report of the German Environment Agency relies on up to 120,000 measurements per parameter from 2,507 water supply areas. Almost all of the 14 microbiological and chemical parameters examined were complied with in more than 99 percent of cases. The highest exceedance rate concerned coliform bacteria as an indicator parameter, at 1.1 percent of samples in 2022 – indicator bacteria whose detection triggers a follow-up examination and does not automatically mean a health hazard.

The weak point is rarely in the network. Exceedances of the limit for nitrate were the rare exception, and for lead they occurred mainly at the consumer’s tap, that is, in the building’s plumbing. That is exactly where an individual check makes sense.

Why filtering is not the solution

Activated carbon and ion exchange filters remove chlorine, flavor substances and hardness minerals. A physiological benefit of this is not defined, because the starting quality already meets the limits. The mechanism that actually is described runs in the other direction: filters retain organic material that serves bacteria as a breeding ground, and they stand at room temperature. The German Environment Agency therefore writes verbatim that it advises against the use of these devices.

The Verbraucherzentrale (German consumer advice centre) reaches the same conclusion and states that from a health perspective the use of filters for tap water is generally not necessary; Stiftung Warentest rated water filters in 2022 as superfluous to harmful. Claims about harmonizing or energizing water cannot be scientifically substantiated.

Demineralizing and remineralizing

Reverse osmosis removes almost all dissolved substances, including calcium and magnesium. The WHO has summarized the consequences of permanently very low-mineral water in a chapter of its own: increased diuresis with greater excretion of sodium, potassium, chloride, calcium and magnesium, losses of up to 60 percent of magnesium and calcium during cooking, because low-mineral water draws these substances out of the food being cooked, and a corrosive effect on pipe materials with increased uptake of heavy metals. As desirable, the chapter names at least 10 mg/l magnesium and 20–30 mg/l calcium.

Remineralization with salt does not solve this. According to tests by Stiftung Warentest, Himalayan salt consists of 97 to 99 percent sodium chloride, ordinary table salt of about 98 percent; despite the advertising with 84 minerals, the Bavarian State Office for Health and Food Safety found only eight additional minerals, mostly in very small amounts. Anyone who adds table salt to demineralized water adds sodium, not calcium or magnesium.

What the studies show

Does drinking more do anything at all

Systematic review of randomized trials on daily fluid intake: of 1,464 records screened, 18 studies met the inclusion criteria, with intervention durations between 4 days and 5 years. Positive findings were reported for weight loss and for kidney stones, with 15 fewer events per 100 participants over 5 years. Ten of the 18 studies reported at least one positive result, eight negative ones. The authors’ conclusion: the quantity and quality of the evidence are limited.

Water and weight in overweight people

Meta-analysis of eight randomized trials: body weight WMD −0.33 kg (95 % CI −1.75 to 1.08; I² = 78 %), BMI −0.23 kg/m² (95 % CI −0.55 to 0.09), waist circumference 0.05 cm (95 % CI −1.20 to 1.30). None of the three endpoints reached significance.

The counterposition to the WHO assessment

The German Federal Institute for Risk Assessment has assessed mineral water with very low mineral content and concludes that with a balanced diet and normal fluid intake, no side effects are recognizable that would argue against its use. It recommends caution with a very unbalanced diet, for vegans and people with lactose intolerance, for pregnant and breastfeeding women, and for athletes with exercise lasting more than 1.5 hours.

Where the data stop

There is no study that has tested filtered against unfiltered German tap water on a health endpoint. The statement that an added benefit has not been established refers to this absence and not to a negative finding. Conversely, the warning about microbial contamination is also an official assessment and not a quantified risk estimate: how often it actually happens and with what consequences, the source does not say. For reverse osmosis in the home followed by remineralization, there is no study with a health endpoint – neither for benefit nor for harm.

The WHO target values for magnesium and calcium also come from a review chapter, not from randomized trials, and they are intended for the drinking water supply of entire populations. On microplastics in drinking water, no study could be found that links a health endpoint in humans to intake via drinking water: figures on particle concentrations exist, effect data do not.

How to do it

Check instead of filter is the robust short version. Let the first water in the morning run until it comes out of the tap cool – especially with chrome-plated fittings, from which nickel can leach, and in older installations. Have the building’s plumbing checked if the building was built before 1973 or lead pipes are suspected; that is the justified case for an analysis, not for a filter device. If you filter for taste reasons, change the cartridge according to the manufacturer’s instructions, store the water cool and use it promptly. On quantity: the DGE gives as a guideline for total water intake 2,600 ml/day for 25- to 51-year-olds, of which 1,410 ml come from beverages; the rest comes from solid food and oxidation water. The common two to three liters of drinking water are considerably higher.

Safety

With lead pipes the matter is clear: water from them is always unsuitable for pregnant women, infants and children up to the age of six, and complete replacement of the pipes is absolutely necessary. Filters are not a solution for this. For people with a weakened immune system, the risk of microbial contamination from cartridges that are not changed is more relevant than for healthy people. And drinking too much is a real, if rare, risk: a systematic review of 177 publications with 590 patients found a median intake of 8 liters per day and a median serum sodium of 118 mmol/l at presentation; 31 percent had no underlying condition. With heart or kidney failure, the fluid intake set by a physician applies in any case.

Sources

• Umweltbundesamt (German Environment Agency), quality of drinking water from central supply systems 2020–2022
• Umweltbundesamt (German Environment Agency), TrinkWas guide
• Verbraucherzentrale (German consumer advice centre), water filters from a hygiene perspective
• Verbraucherzentrale (German consumer advice centre), Himalayan salt
• Kozisek F, WHO, Nutrients in Drinking Water 2005
• German Federal Institute for Risk Assessment (BfR), Opinion No. 041/2020
• German Nutrition Society (DGE), reference values for water
• Rangan GK et al., BMJ Open 2021