Water filters: Questions and answers

It depends on what you want to achieve. A reverse osmosis system removes almost everything, including contaminants and minerals. It requires electricity, a water connection and produces waste water. An activated carbon filter with PI technology, such as the one used by MAUNAWAI, reliably removes contaminants whilst retaining the minerals in the water. It works without electricity, without installation and without wasting water. If you want clean, mineral-rich water that your body can utilise effectively, a good water filter is the more natural choice. Osmosis is more suitable for specialist applications, such as when the source water is extremely contaminated.

This is something many people notice. A plausible explanation: osmosis water is ‘empty’. It contains no minerals, which are important for the body’s water absorption. After drinking it, your body continues to seek out the minerals that should come with the water. This can manifest as a persistent thirst. Mineral-rich water, on the other hand, quenches your thirst more quickly because it gives the body what it expects. Anyone who has ever drunk from a mountain spring will know this feeling: a sip that really satisfies.

The body needs electrolytes for almost all metabolic processes. Calcium, magnesium, potassium and sodium are not mere additives, but essential for nerve function, muscle activity and cellular transport. In its report on minerals in drinking water, the WHO states that long-term consumption of water low in minerals can lead to fatigue, weakness, headaches and, in rare cases, metabolic acidosis. 
A large Swedish cohort study involving 26,733 women also showed that drinking water with higher magnesium and calcium content was associated with a lower risk of stroke. With a balanced diet rich in fruit and vegetables, the mineral deficit caused by drinking osmosis water can be at least partially offset.

There are three reasons against it. Firstly, reverse-osmosis water no longer contains any minerals, including calcium and magnesium. These are part of the body’s natural water supply. Secondly, demineralised water has an acidic pH and can disrupt the body’s electrolyte balance. Thirdly, reverse-osmosis water does not keep well. Because it lacks an internal structure, it absorbs substances from plastic or glass containers. Anyone who drinks osmosis water on a regular basis and does not eat a particularly mineral-rich diet risks a deficiency that is difficult to rectify.

In a detailed report, the World Health Organisation has found that long-term consumption of demineralised water can have adverse effects on the body’s mineral and water balance. In the study, WHO scientist Frantisek Kozisek explains that water low in minerals can flush electrolytes out of the body. The German Nutrition Society and many scientists therefore warn against the exclusive use of demineralised water, which includes osmosis water. In the case of an unbalanced diet, drinking water low in minerals can upset the body’s electrolyte balance. Anyone who drinks osmosis water should therefore take particular care to ensure they have a mineral-rich diet.

Reverse osmosis systems filter out not only harmful substances but also valuable minerals. The water becomes demineralised and acidic (pH value around 4.5 to 5.0). It cannot be stored because it absorbs substances from the containers. The World Health Organisation points out that demineralised water also has a corrosive effect: it leaches metals from pipes and containers. There are also practical drawbacks: osmosis systems require electricity and a water connection, and produce a significant amount of waste water. For every litre of filtered water, there are typically three to five litres of rinse water. The purchase and maintenance costs are also significantly higher than for a gravity filter.

In practice, ‘reverse osmosis’ is simply the technically correct term for standard domestic osmosis systems. Both terms refer to the same process: tap water is forced under pressure through a very fine membrane that retains almost all dissolved substances. So when someone says ‘osmosis system’, they usually mean reverse osmosis. The original term “osmosis” comes from biology and describes a natural process within cells. In water treatment, this process is technically “reversed”, hence the name.

This question arises particularly when people are referring to reverse osmosis water. With a good activated carbon filter that retains minerals, there are no health-related reasons against drinking it daily. On the contrary: reducing pollutants is beneficial, as is retaining the minerals. Problems only arise when filters are used incorrectly: left in place for too long without being replaced, storing the filtered water incorrectly, or using reverse osmosis systems that remove all minerals. Anyone who regularly maintains a certified, high-quality filter and consumes the filtered water promptly is drinking high-quality water.

Filters are safe provided they meet two conditions.
Firstly, they must be proven to remove the relevant contaminants from the water. Look for independent tests and studies, not just advertising claims.
Secondly, the filter material itself must not release any undesirable substances into the water. In Germany, the list set out in Section 20 of the Drinking Water Ordinance of the Federal Environment Agency regulates which treatment substances and filter media are approved for drinking water treatment. It is also important to change the filter cartridges regularly. A filter that remains in use for too long becomes a source of contamination itself. Reputable manufacturers clearly state when the filter needs to be replaced.

If water has been standing in your home’s pipes for more than four hours (stagnant water), substances may leach out of the pipes. These include small amounts of copper, zinc or, in older buildings, lead.
The Federal Environment Agency therefore recommends: let water that has been standing in the pipes for four hours or longer run for a short while until it feels slightly cooler to the touch. 
The finger test is a reliable method: fresh water is noticeably cooler than stagnant water. This recommendation applies particularly after getting up, after a holiday or after prolonged absences. Baby food should never be prepared using stagnant water.

The independent consumer organisation Altroconsumo puts it this way: apart from a few isolated cases, tap water tastes good, is healthy and is subject to quality controls. So you needn’t be afraid to drink it. Mineral water, on the other hand, has a significant environmental footprint: production, transport, plastic waste. High-quality mineral water costs quite a bit per litre, whereas filtered tap water costs around 12 cents. The answer therefore depends on what matters to you. Taste, the environment, price: on all three counts, filtered tap water comes out on top for most households.

Basically, nothing. Tap water in Central Europe is perfectly safe to drink and well regulated. What bothers many people is more the taste: chlorine, limescale or a metallic aftertaste from the pipes in their homes. Added to this are concerns that are statistically minor but cannot be ruled out: agricultural residues, PFAS in certain regions, old domestic plumbing, and microplastics. If you want to play it safe without switching to plastic bottles, a filter is a good option. You should only avoid tap water completely in exceptional cases, such as following contamination warnings from your water supplier.
Read more in the article ‘Drinking tap water – yes or no?’.

In Germany, Austria and Switzerland, tap water is one of the most strictly regulated foodstuffs of all. The Federal Environment Agency confirms that more than 99 per cent of test results meet or exceed the requirements of the Drinking Water Ordinance. Nevertheless, there are good reasons to use a filter. Firstly, the limit values do not cover everything. With the new Drinking Water Ordinance of 2023, PFAS and bisphenol A have only recently been regulated at all. Secondly, a lot happens on the journey from the waterworks to your tap: old pipes, domestic plumbing, and possibly lead pipes in older buildings. A good filter is insurance against what the statistics do not show.

The MAUNAWAI Kini has been named the top performer in multiple tests conducted by Altroconsumo, Italy’s largest independent consumer organisation. In a comparative test against 14 other water filter jugs, the Kini achieved the best results for all contaminants tested. It reduced nitrates by 79 per cent, removed 100 per cent of the solvents and trihalomethanes tested, and did not excessively soften the water. The test laboratories particularly praised the fact that the Kini removes contaminants without stripping the water of its beneficial properties.
When 14 water filters go head to head

Like any filtration technology, ion exchange has its own particular characteristics. Firstly, the process slightly increases the sodium content in the water because calcium and magnesium are exchanged for sodium. This is something to bear in mind if you are following a low-salt diet. Secondly, the filter’s design focuses on water hardness and chlorine. PFAS, pharmaceutical residues and microplastics fall outside this scope. Thirdly: the short replacement intervals of around four weeks mean regular ongoing costs and require discipline in everyday life. If the replacement schedule is adhered to reliably, this is easily manageable. More advanced solutions are now available for a broader filter spectrum with longer intervals.

Brita is a well-established brand with a long history and a clear profile. Its classic cartridges use ion exchange and are primarily designed to tackle water hardness and chlorine. If that’s exactly what you’re looking for, Brita is a good choice. Other requirements fall outside the filter’s scope: contaminants such as PFAS or microplastics are not covered, and the ion exchange process partially replaces calcium and magnesium with sodium. If you’re looking for a broader range of filtration while retaining natural minerals, you’d be better off looking at other systems. It’s less a question of better or worse, and more about finding the right solution for your needs.

There is no single ‘best filter in the world’, as it depends on what you want to filter, how hard your water is, and which design suits your needs. What can be objectively measured, however, is filter performance in independent tests, research on the reduction of harmful substances, and the retention of minerals. The MAUNAWAI Kini has been a multiple test winner at Altroconsumo and was tested in a 12-month long-term study at the IIREC in Graz. For families with hard water who want mineral-rich, low-contaminant drinking water, it is one of the best possible choices in this design.

In terms of units sold, Brita is the market leader in Europe for water filter jugs. This position has been built up over decades, thanks to a clear product range and high brand awareness. Anyone looking for a filter often thinks of Brita first. However, market leadership and coming top in tests are two different things. In independent comparison tests, smaller suppliers sometimes perform better in terms of filter performance. The MAUNAWAI Kini, for example, is a multiple test winner at Altroconsumo, but in terms of sales figures, it is a niche product. Both have their merits. What suits you depends on what you expect from the filter.

It would be misleading to give a blanket answer, as different filters are more or less effective at removing different groups of substances. In the independent Altroconsumo test, the MAUNAWAI Kini achieved the best overall performance: 100 per cent reduction in solvents and trihalomethanes, and 79 per cent in nitrates. In a separate DAkkS-accredited laboratory study conducted by the Potsdam Water and Environment Laboratory, our filter system removed over 99.99 per cent of all ten PFAS substances tested. They were no longer detectable after filtration. 
PFAS are particularly relevant because the European Food Safety Authority has set a very low tolerable weekly intake: 4.4 nanograms per kilogram of body weight for the sum of the four most important compounds.
Important: Pay attention not only to what a filter removes, but also to what it retains.

Still tap water does not usually cause heartburn. On the contrary: water helps to dilute the acid in the stomach and is usually the first thing recommended for mild heartburn. Heartburn is more likely to be triggered by carbonated mineral water, coffee, alcohol, or fatty or spicy foods. If you regularly experience heartburn after drinking tap water, this is rarely due to the water itself. It is more likely to be caused by the temperature (ice-cold water can irritate some stomachs) or a sensitive stomach lining. In this case, speak to your GP.

It depends on the filter. With a good activated carbon filter that retains minerals, exactly what you want happens: you consume fewer harmful substances whilst retaining the valuable minerals. Your body gets calcium and magnesium from the water, and your electrolyte balance remains stable. It’s different with reverse osmosis water: this lacks minerals, which can lead to a deficiency if consumed over the long term and combined with an unbalanced diet. In short: filtering makes sense, but it’s the ‘how’ that matters. Living, mineral-rich water is the natural choice; demineralised water is more of a stopgap solution.