Pharmaceutical residues in drinking water: contamination and filtration

Pharmaceutical residues can be detected in German drinking water. The quantities amount to a few nanograms per litre. A nanogram is 1 billionth of a gram. The Umweltbundesamt (German Environment Agency) sees no risk in this for any age group. To this day, the Trinkwasserverordnung (German Drinking Water Ordinance) does not specify a limit value for pharmaceuticals. Anyone who wants to reduce the residual amount at home can filter it out with activated carbon.

By 2021, laboratories had detected 414 pharmaceutical active substances in water. In Germany, around 3,000 active substances are approved, spread across more than 9,000 products. They come from human and veterinary medicine. A broad spectrum is found, spanning all areas of application.

The most frequently discussed substance is diclofenac. In high doses, the active substance is available on prescription only. In small doses, it is sold over the counter in ointments. Diclofenac has already been detected in sewage sludge, surface water, groundwater and drinking water. Experts also attribute the mass death of vultures in India and Pakistan in the 1990s to it. Kidney damage in rainbow trout can likewise be traced back to this input.

Ibuprofen breaks down more easily and is less harmful to the environment. However, consumption has risen sharply in recent years. As a result, ibuprofen now turns up in drinking water in places, so far in trace amounts. Antibiotics such as sulfamethoxazole enter the water cycle from human medicine and livestock farming. On top of this come hormones such as ethinylestradiol from the contraceptive pill, via natural excretion.

Pharmaceutical residues can be filtered out of drinking water with activated carbon. An activated carbon block filter binds the dissolved drug molecules to its porous surface by adsorption. A single gram of high-quality activated carbon provides around 1,500 square metres of internal surface area for this.

Adsorption refers to the accumulation of foreign substances on a surface. In the filter, the water takes a long path through a labyrinth of pores. Along the way, dissolved molecules stick to the walls and accumulate there. This effect works particularly well with pharmaceuticals. This is because most active substances have an organic structure and readily bind to carbon. Minerals such as calcium, magnesium, sodium and potassium, on the other hand, remain in the water. The article What is activated carbon? explains how the material is structured.

The design is decisive. Loose granular activated carbon lets the water flow around the granules. It therefore binds only a small proportion of the residues. An activated carbon block filter compresses the carbon into a solid block. The water has to pass through its fine channels. Sintered activated carbon binds the most. It has additionally been compacted under heat and pressure. All designs are compared in the guide Activated carbon filters for water.

For the home, Alb Filter uses the ACTIVE+ activated carbon cartridge. It works mechanically, adsorptively and catalytically. According to the manufacturer, it reduces pharmaceutical residues, hormones, pesticides, lead and copper. Its pores measure 0.7 µm and also retain microplastics. The cartridge delivers 3,000 to 5,000 litres or lasts around 4 months. After that, it is exhausted.

There are 2 methods that work against pharmaceutical residues: activated carbon block filters and reverse osmosis. Ultrafiltration, UV disinfection and boiling do not remove the active substances. Anyone who specifically wants to remove pharmaceuticals from tap water needs a method that binds or retains dissolved organic molecules. UV stands for ultraviolet light.

UV treatment does not remove pharmaceuticals from water. According to the DVGW, UV disinfection is the only physical disinfection method approved in Germany for public water treatment. UV-C radiation damages the genetic material of bacteria and viruses and thus eliminates them. Pharmaceuticals remain unaffected. The usual doses do not break down their molecules. Only advanced oxidation attacks micropollutants. This combines UV light with an oxidising agent. Such systems are found in waterworks, not in private households.

The same applies to ultrafiltration (membrane filtration). The NANO cartridge uses its membrane to retain bacteria, germs and legionella. The guide to bacteria in tap water describes this in detail. Such a membrane does not help against dissolved pharmaceuticals. Its pores are too coarse, as the molecules are smaller. Table-top jug filters with loose granules improve taste and odour. They do little against pharmaceutical residues, and there is a risk of germ contamination in jug filters. The Drinking water filters page provides an overview of all systems.

Pharmaceutical residues enter the water cycle via 2 main routes. The first route is waste water from households and hospitals. The second route is via slurry and fertiliser from agriculture. The input occurs at specific points at individual discharge sites and diffusely over large areas. Both routes end up in surface waters and groundwater.

Whether a pharmaceutical harms the environment depends on the individual active substance. Substances that have 3 properties at once are problematic: persistent, mobile and toxic. Persistent means hard to break down. Mobile means easily carried along in water. Toxic means poisonous to humans, animals or the environment.

Since 2006, every newly approved medicine has undergone an environmental risk assessment. It examines exactly 3 factors: degradability, transport and toxicity. For older active substances dating from before 2006, on the other hand, there are hardly any data. Mixture effects have also been little researched. This refers to the interaction of several pharmaceuticals in the same body of water. As a result, some of the environmental effects remain unknown to this day.

Conventional wastewater treatment plants retain pharmaceutical residues only partially. Their 3 treatment stages are not designed for this. They remove 60 to 80% of ibuprofen. For the X-ray contrast agent iomeprol, the figure drops to 40 to 50%. The rest passes through the treatment plant and flows into the receiving water.

A fourth treatment stage provides a remedy. It uses ozonation and activated carbon, sometimes in combination. Such processes remove up to 90% of micropollutants. So far, only a few plants operate such a stage.

The EU Urban Wastewater Treatment Directive changes this (Directive (EU) 2024/3019). It entered into force on 1 January 2025. All wastewater treatment plants with 150,000 population equivalents or more will need a fourth treatment stage by 2045. In risk areas, the obligation already applies from 10,000 population equivalents. In line with the polluter-pays principle, manufacturers of pharmaceuticals and cosmetics bear at least 80% of the costs. EU countries must transpose the directive into national law by 31 July 2027.

A second problem remains even with a fourth stage. Sewage sludge is often used as fertiliser. If it ends up on fields, the bound pharmaceutical residues migrate through the soil into the groundwater. From there, they reach drinking water.

Consumption of human medicines in Germany will grow by around 70% by 2045. This forecast comes from a 2017 study by civity Management Consultants commissioned by the BDEW. The driver is demographic change, i.e. the ageing population. After all, per capita consumption rises significantly with age.

Today, the quantity of medicines in tap water is considered harmless. With an increase of 70%, however, this calculation shifts. That is, provided that wastewater treatment plants and prescribing practices stay the same. This is precisely what the fourth treatment stage and the EU's extended producer responsibility aim to address.

Consumers have 4 levers: disposing of old medicines correctly, using self-medication in moderation, avoiding stockpiling and using a drinking water filter at home. The filter reduces contamination at the tap. The other 3 reduce the input into waste water.

Old medicines should never go down the toilet or the sink. From there, the active substances go straight to the wastewater treatment plant. It retains only some of them. Old medicines are disposed of correctly via household waste, via pharmacies on a voluntary basis, or via mobile hazardous waste collections, collection points or recycling centres.

Besides consumers, 3 other players are called upon. Policymakers and the water sector can treat hospital waste water separately, add a fourth treatment stage to wastewater treatment plants and set limit values for pharmaceutical residues in water. The healthcare sector can take the environment into account as early as the development stage, adapt prescribing practices and promote alternative therapies. Agriculture can apply fertiliser close to the ground and in line with the weather, use less slurry and handle veterinary medicines with care.