Water Filters for Tap Water: When a Filter Makes Sense and What Each Technology Removes

Does a water filter make sense? The short answer

In short: For water from the public supply, a filter is usually not necessary from a health perspective. But there are clear exceptions.

Have you ever wondered how many checks your glass of water has been through before it comes out of the tap?

Germany's Federal Ministry of Health and the German Environment Agency regularly evaluate the data from the federal states. The current drinking water report covers the years 2020 to 2022. It looks at the large supply zones that deliver more than 1,000 cubic metres per day or supply more than 5,000 people. There, for most microbiological and chemical parameters, more than 99 percent of samples met the requirements of the Drinking Water Ordinance (Trinkwasserverordnung, TrinkwV), Germany's legally binding regulation on drinking water quality.

The Drinking Water Ordinance requires its standards to be met at the point where the water comes out of the tap inside the building. The pipes inside the building are the owners' responsibility. What happens after that in your filter jug is in your hands.

Imagine the waterworks as a strictly inspected commercial kitchen. Whether the food reaches you in good shape also depends on the tray it is carried on for the last few metres. With drinking water, that tray is the plumbing in your building.

If water stands in the pipes for a long time, it can take up substances from pipes and fittings. That is why the German Environment Agency advises against using the first water after a long standing time for drinking or cooking. Let it run until it comes out of the tap cool. How much you should drink at all is a separate question. You can read more about it in the article on kidneys and water.

When a filter can make sense and when it can't

And now you know why a filter only makes sense once you know what it is supposed to protect you from.

What do the PFAS limits in force since 2026 mean?

In short: Since 12 January 2026, a joint limit value has applied to 20 PFAS. From 12 January 2028, a stricter value for four PFAS will be added.

Forever chemicals. The word alone sounds like a problem that will never go away. Maybe you read it in a headline and wondered whether it is in your glass too.

PFAS stands for per- and polyfluoroalkyl substances. The term covers thousands of industrially manufactured chemicals. Their carbon chains are fully or partly bonded to fluorine, and this bond is extremely stable. That is why PFAS are found in non-stick coatings, outdoor clothing, firefighting foam and packaging. And that is why they barely break down in the environment.

Imagine a chain wrapped all round in a suit of armour made of fluorine. Light, water and bacteria can hardly find a spot where they can get a grip.

The deadlines at a glance

What lies behind the two sums? The Sum of PFAS-20 covers 20 PFAS with carbon chains of different lengths, including short-chain ones. With it, Germany implements the EU Drinking Water Directive, which sets 0.10 micrograms per litre for these 20 substances. The Sum of PFAS-4 covers only PFOA, PFNA, PFHxS and PFOS. Individual values below the limit of quantification are not counted in either sum. From 2028, both limit values must be met at the same time.

How small are these amounts? 0.02 micrograms are 20 nanograms, in other words 20 billionths of a gram per litre. That roughly corresponds to a sugar cube of about three grams spread across around 60 Olympic swimming pools.

Why do lawmakers regulate such tiny amounts? Because some PFAS stay in the body for years. For PFOA, follow-up studies from Germany show that blood levels fall only slowly after an exposure has ended.

Why these four substances in particular?

In 2020, the European Food Safety Authority (EFSA) set a tolerable weekly intake for exactly these four PFAS: 4.4 nanograms per kilogram of body weight per week. It considered effects on the immune system to be the most sensitive endpoint. The German Federal Institute for Risk Assessment estimates that the average intake in Germany is in the range of this value. For about half of adults, it is above it.

According to the BfR, PFAS are taken up largely through food and drinking water. In the EFSA assessment, fish, fruit and eggs made the largest contribution among foods. So a water filter can only influence the share that comes from the tap.

What has already happened in Germany

Local contamination happens in Germany too. In 2006, PFOA was found in the drinking water of Arnsberg in the Sauerland region, at 500 to 640 nanograms per litre. For comparison: today's limit value for the Sum of PFAS-20 is 100 nanograms per litre. Around 40,000 people were affected, and their PFOA blood levels were 4.5 to 8.3 times higher than those of comparison groups. In July 2006, activated carbon filtration at the waterworks lowered the levels in the water, mostly to below the limit of detection. In the blood, they then fell by only about 10 to 20 percent per year.

And what if your supplier is above the limit value? Then it must inform the health authority and investigate the cause. The health authority can authorise a temporary deviation if no harm to health is to be expected. To do so, it sets an action value (Maßnahmenwert), the maximum level permitted during this period, and a deadline that may not exceed three years. If the deviation is not expected to be remedied within 30 days, the affected households must be informed and particularly vulnerable groups must be advised.

What does that mean for you? Check your supplier's website for the PFAS values. If the limit value is exceeded or a deviation has been authorised, follow the health authority's advice first. Only after that does the question of a filter arise. You can read further below which technology may be suitable for this.

And now you know why a PFAS value in the water is first a task for the waterworks and only then a question for your kitchen.

Lead pipes at home: why is replacement what counts, not a filter?

In short: Lead pipes have been banned since 12 January 2026. Where they are still in place, the German Environment Agency calls for replacement, not a filter.

An old building, high ceilings, creaking floorboards. And somewhere behind the wall, a pipe that may be older than your grandparents.

According to the German Environment Agency, lead pipes were laid in parts of Germany until 1973, either as the service connection to the building or as pipes inside it. Southern Germany was practically always free of them. Elsewhere, too, far from all older buildings were affected, and most lead pipes have since been replaced. Where water still flows through lead, it usually does not meet the limit value. In water that has been standing in the pipes, the limit is often exceeded many times over.

Why is this so serious? Lead can cause harm even in very small amounts. It accumulates in the body and can impair above all the development of the nervous system and the formation of blood. Unborn babies, infants and toddlers are particularly at risk. In adults, some of the lead is stored in the bones. In phases of increased metabolism, such as pregnancy, it can return to the blood.

The US city of Flint shows how quickly water can become a source of lead. It switched to a more corrosive water source without adequate corrosion control for its old pipe network. Afterwards, the proportion of children under five with elevated blood lead rose from 2.4 to 4.9 percent, as a team led by Hanna-Attisha showed.

What the Ordinance has required since January 2026

The Drinking Water Ordinance required the operators of a building's water system, usually the owners, to remove or decommission lead pipes by the end of 12 January 2026. Residents must be informed without delay if lead pipes are present or suspected. Since 13 January 2026, they must also be told in writing that the obligation has been met or that the deadline has been extended. The health authority can only grant an extension in narrowly defined cases. Owners who fail to act commit an administrative offence, and the health authority can order the replacement.

And a filter as a stopgap?

In the USA, certified filters are often handed out when there are lead problems, as a bridge until the pipes are replaced. What do they achieve?

Where filters failed, the review attributed this, among other things, to very high lead levels, to the shape and size of the lead particles, and to incorrect operation and lack of maintenance.

Both fit together. A certified filter can hold back lead in tests. But it leaves the source in the wall, needs maintenance and brings its own hygiene problem. And in Germany, replacement is mandatory anyway.

How to recognise lead pipes

If you rent, ask your landlord first. The property management may also know the year of construction and the material. If the answer is unsatisfactory, your local health authority is the next port of call. If the situation remains unclear, a water test can bring clarity. You will have to pay for it, and the water should have stood in the pipes for at least four hours beforehand.

I describe what lead can do in the body and how it is measured in the article on lead poisoning, its sources and symptoms.

And now you know why, if you suspect lead, your first step is a call to your landlord, not the purchase of a filter.

Which filter technology holds back what?

In short: Jug filters, activated carbon blocks and reverse osmosis do very different things. No device holds back everything, and each one needs care.

In the shop, they stand side by side: the jug, the attachment for the tap, the system that goes under the sink. They all promise pure water. But pure of what?

Two principles lie behind most devices. The first is activated carbon. Imagine it as a sponge with a huge inner surface. Just one gram can have several hundred square metres of internal surface area to which substances stick.

The second is a membrane. In reverse osmosis, water is forced under pressure through an extremely fine layer. Most dissolved substances stay behind, including the minerals.

In real-world use, a team from the Chinese Academy of Sciences measured removal rates of 21 to 99 percent for 14 PFAS in household filters with activated carbon made from coconut shells. How well a substance stuck depended mainly on how water-repellent it is.

So look for independent testing for exactly the substance you are concerned about. And plan for maintenance from the start. It is as much a part of the device as the filter itself.

And now you know why the most important question when buying a filter is not which one is best, but what exactly it is supposed to protect you from.

When does the filter itself become the problem?

In short: Activated carbon not only traps substances, it also offers bacteria a habitat. A forgotten filter can release more germs than were in the tap water.

Back to the jug on the worktop. The cartridge from the spring is still filtering, and the water tastes the same as always. What is happening inside it?

Tap water is not sterile, and it doesn't need to be. It contains a few, mostly harmless bacteria. In the activated carbon, they find a huge surface and nutrients that the carbon itself has fished out of the water. Room temperature and long standing times can make life even easier for them.

In the household filters, levels reached up to 6,000 colony-forming units per millilitre. Even the material of 5 of the 13 new filters examined was already contaminated with bacteria or moulds. The study is old, and filters have changed since then. But more recent work shows a similar pattern.

A field study by the University of North Carolina in 17 households with their own wells found another pattern. When little water flowed through the activated carbon filter overall, the odds of finding coliform bacteria in the filtered water were more than 50 times higher.

And what about the silver that is added to some filters? In a 1981 lab study, silver-containing activated carbon did slow down coliform germs, but not the growth of the other bacteria.

There is a similar pattern with chemicals. A full sponge absorbs nothing more, and if you squeeze it, it gives back what it has taken in. The researchers from Genoa point out that poorly maintained activated carbon could even increase PFAS levels in the filtered water.

This very hygiene problem is also the reason why the German Environment Agency advises against filters for lead pipes.

If you filter: how to keep the filter your tool

• Change the cartridge at the latest after the time or number of litres the manufacturer specifies, whichever comes first.
• Clean the jug and lid regularly.
• Drink filtered water promptly and don't leave it standing for days.
• After longer breaks, such as a holiday, it is better to put in a new cartridge.
• If you hardly use the filter, doing without it can be the better choice.
• If your immune system is weakened, during pregnancy and for infants, talk to your doctor or midwife first.

And now you know why the cartridge from the spring is no longer a safety bonus but an open question.

Reverse osmosis and minerals: is purer automatically better?

In short: Reverse osmosis can hold back PFAS almost entirely. But it also strips the water of calcium and magnesium.

Pure water. That sounds like the ultimate ideal. But do you want water in which practically nothing is dissolved any more?

Calcium and magnesium, which make water hard, are dietary minerals. Most of them usually come from food. But hard water can make a contribution. Your supplier can tell you how much of them your water contains: it must publish hardness, calcium, magnesium and potassium online.

An observational study from Chongqing with almost 30,000 schoolchildren found smaller gains in height and more tooth decay at schools with low-mineral water from reverse osmosis systems. Such ecological studies cannot reliably rule out confounding factors. They are a hint, not proof.

Then there are practical points. Depending on the device, part of the water flows unused into the drain as concentrate. And pre-filter, membrane and, if present, storage tank need regular care, otherwise the same hygiene questions arise as with the jug.

If reverse osmosis makes sense for you, for example with proven PFAS contamination, pay all the more attention to a mineral-rich diet with vegetables, pulses, nuts and whole grains.

And now you know why the purest technology is not automatically the best choice for your everyday life.

Microplastics in tap water: how much is there?

In short: Measurements found only very few microplastic particles in tap water from well-treated groundwater. But these methods do not capture the smallest particles.

Plastic in the blood, plastic in the brain. After headlines like these, you may look at your tap differently.

A team from Aalborg University recorded particles from 6.6 micrometres upwards in drinking water networks. It estimated the possible intake via tap water at less than one particle per person per year, provided the water comes from an efficient waterworks.

A paper from Wageningen, in which the World Health Organization was involved, shows how cautiously such figures need to be read. The team assessed 50 studies on microplastics in freshwater and drinking water. The measured amounts differed by ten orders of magnitude, and only four studies met all quality criteria. On top of that, the measurements mentioned only capture particles above a certain size. They say nothing about even smaller particles.

I describe how bottled water compares and which everyday sources carry more weight in the article on microplastics in the body. I have not found any robust study on whether a household filter further lowers the already small amount in German tap water.

And now you know why, for German tap water, microplastics alone are not a strong argument for a filter.

How do you check your water and your pipes? Three steps

In short: Two pieces of information answer most questions: your water supplier's values and the age of your pipes.

You don't want a guess, you want clarity. The good news: much of it is only a few clicks and one conversation away.

1. Read your supplier's values

   Under Section 46 of the Drinking Water Ordinance, water suppliers must publish current test results online, each with the limit value and testing frequency. As a rule, the results may not be more than a year old. They also include hardness, calcium, magnesium and potassium. Since the PFAS limit value came into force, values for the Sum of PFAS-20 should be listed there too. If you make a justified request, you can also get the information free of charge in other ways.

2. Check your building's plumbing

   Ask when the building and its pipes were built, and take a look at visible pipes in the basement. For a building from before 1973 outside southern Germany, a close look is particularly worthwhile, for example in an old Berlin apartment building (Altbau). The waterworks' values say little about lead in your building, because lead comes mainly from pipes and components inside the building.

3. Have it tested if questions remain

   Commission an approved testing laboratory if you are unsure. For lead, the water should have stood in the pipes for at least four hours beforehand. The health authority can tell you which test makes sense in your situation.

And now you know why your supplier's website and a look in the basement can bring more clarity than any test mark on a package.

What do the four KPNI lenses show, and what does that mean for you?

In short: The substances that matter in drinking water touch all four major regulatory systems. That is a reason for care, not for fear.

Perhaps you are now wondering: if so much is well regulated, why look so closely at all?

In clinical psychoneuroimmunology, KPNI for short, I look at four systems that are constantly talking to each other: the nervous system, the immune system, metabolism and the hormonal system. For drinking water, this results in a clear picture, but in some places also in open questions.

I describe the connection between PFAS and hormones in more detail in the article on PFAS as a hormone topic.

For me, this is where the biggest gain lies. You don't have to look at every glass of water with suspicion. And you don't have to buy every device that promises pure water. Freedom here means knowing the two questions that are usually enough: what does my supplier say? And what is inside my walls? Fear narrows your world. Knowledge brings calm.

I describe what detox in everyday life can look like without a programme in the article on gentle everyday detox.

And now you know why composure and care go well together when it comes to drinking water.

Further reading