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Lead is a toxic heavy metal that was once commonly used in water pipes, solder, and fixtures. It can leach from old plumbing and enter drinking water, especially when water sits in the pipes for a long time. Lead accumulates in the body and is considered neurotoxic. Fetuses, infants, and children are particularly at risk, as lead can impair brain and nervous system development and lower IQ. In adults, it can also damage the cardiovascular system, kidneys, and blood formation. As a precaution, lead levels in [trinkwasser] should be as close to zero as possible.

Hormones in drinking water are usually minute traces of natural or synthetic signaling substances that originate from medications, contraceptives, livestock farming, or industry. They enter surface waters and groundwater via wastewater, manure, and precipitation. Many wastewater treatment plants are unable to completely remove these micropollutants. The primary focus is on hormone-active substances that can affect the endocrine system, such as estrogen-like compounds. Risks under discussion include changes in fertility, developmental disorders, and effects on the thyroid and metabolism.

Copper is an essential trace element and a component of many water distribution systems, primarily in the form of copper pipes. In small amounts, copper is important for the human body; however, in excessively high concentrations, it can lead to gastrointestinal complaints, nausea, vomiting, and, in the long term, liver or kidney damage. Elevated copper levels in drinking water are usually caused by corrosion of copper pipes, particularly in soft or acidic water, newly installed pipes, or water that has been stagnant in the pipes for a long time.

Drug residues in drinking water occur when active ingredients from human and veterinary medications enter wastewater treatment plants via feces and urine and from there into rivers, lakes, and groundwater. Many active ingredients are only partially broken down in the body and can be detected in minute traces in drinking water, such as painkillers, antibiotics, blood pressure medications, or hormones. Wastewater treatment plants are often only partially equipped to handle such micropollutants. Risks such as antibiotic resistance, effects on the endocrine system, or long-term effects of mixtures of active ingredients are currently being debated.

Microplastics are tiny plastic particles, usually smaller than 5 millimeters, often even in the micro- or nano-range. They are generated as primary microplastics—for example, in cosmetics, cleaning products, or industry—or as secondary microplastics, when larger plastic pieces break down due to UV light, friction, and weathering. These particles enter rivers, lakes, oceans, and groundwater via wastewater, sewage treatment plants, tire wear, textile fibers, or litter. In drinking water, they are invisible to the naked eye but can be detected.

Micropollutants in drinking water are very small residues of modern everyday, agricultural, and industrial chemicals that can be detected even at the lowest concentrations. These include, among others, pesticides, pharmaceutical residues, hormones, PFAS, industrial chemicals, cleaning agent residues, and other trace substances. They typically enter the water cycle via wastewater, wastewater treatment plants, agriculture, surface waters, or groundwater. Many of these substances are difficult to remove completely, which is why they should be reduced in drinking water as a precautionary measure.

Nitrate is a water-soluble salt of nitric acid that occurs naturally in the soil and is an important nutrient for plants. However, intensive agriculture, fertilizers, and manure cause large amounts of nitrate to enter groundwater and drinking water. Elevated nitrate levels are considered particularly critical for infants because nitrate can be converted into nitrite in the body, which impairs oxygen transport in the blood. In the long term, there is also ongoing discussion about its potential role in the formation of carcinogenic nitrosamines.

Nitrite is an intermediate product in the nitrogen cycle and is formed, among other things, when nitrate is converted by bacteria. In drinking water, nitrite can originate from contaminated groundwater, corrosion in pipes, or disinfection processes. Nitrite is significantly more toxic than nitrate: it can convert the red blood pigment hemoglobin into methemoglobin, thereby impairing oxygen transport in the blood. Infants are particularly at risk. In addition, nitrite can react with certain protein components to form nitrosamines, some of which are considered potentially carcinogenic.

Pesticides are chemical or biological agents used in agriculture, horticulture, and municipal settings to control weeds, insects, fungi, or rodents. These include, among others, herbicides, insecticides, and fungicides. Some of these substances enter groundwater and drinking water via soil, surface water, and drainage systems. Many pesticides are very stable, can accumulate, and can be detected even in trace amounts using modern analytical methods. Some active ingredients and degradation products are suspected of being harmful to health.

PFAS, or per- and polyfluoroalkyl substances, are a large group of synthetic chemicals that repel water, grease, and dirt. They have been used for decades in applications such as outdoor clothing, cookware, firefighting foams, paper coatings, and industrial processes. PFAS are extremely stable, hardly degrade in the environment, and are therefore also called “forever chemicals.” Residues are found worldwide in soil, water bodies, groundwater, and drinking water. Studies link individual PFAS to health risks such as immune system disruption, elevated cholesterol levels, and an increased risk of certain types of cancer.

Heavy metals are high-density metals, some of which are essential—such as copper or zinc—while others can be harmful to health even in small amounts, such as lead, cadmium, or mercury. They enter drinking water primarily through natural rock layers, industrial discharges, corrosion of pipes and fittings, or old household plumbing systems. Typical consequences include a metallic taste, discoloration, and sediment; depending on the metal, there may also be long-term risks to the nervous system, kidneys, liver, cardiovascular system, or child development.