Particle filtration is the first step of the BRITA filtration process, removing particles and reducing turbidity before water passes through further filter stages. The filter fleece acts like a sieve: particles get caught both on its surface and within the fleece itself.

While these particles are usually not harmful to health, they can cause blockages in appliances such as water dispensers, leading to downtime.
All BRITA water filters combine particle filtration with activated carbon. Some models also include an ion exchanger.

An ion exchanger removes certain unwanted ions from the water, such as calcium or magnesium, which can cause limescale deposits by binding them to its surface. At the same time, the ion exchanger releases harmless ions into the water in exchange. This process ensures that only the undesirable ions are removed, while the overall mineral balance of the water is maintained. This technology is used, for example, in the BRITA PURITY C water dispenser filter.

Activated carbon works through adsorption: its natural microporous structure gives it an extremely large internal surface area, allowing it to effectively trap and bind substances from water. BRITA's activated carbon is derived from coconut shells, a renewable source, rather than wood, peat or coal used by some alternatives.

Activated carbon filtration reduces a broad range of substances:

• Organic compounds including PFAS, pesticide residues and industrial paints
• Taste- and odor-affecting substances including chlorine, chlorine compounds and bacterial metabolic products

Activated carbon is a core component of BRITA filters and plays an especially important role in cold water filtration.

Membrane filtration uses a thin, selective layer of material that retains certain particles or molecules while letting others pass through - effectively removing bacteria, microbial cysts, and other impurities to ensure high purity and safety.

BRITA water dispensers use a two-stage membrane filtration system:

• CLARITY Protect: positioned at the inlet, filtering out particles and contaminants as water enters the system
• CLARITY Safe X3: installed directly before the outlet, acting as an additional safety barrier against bacteria right at the point of dispensing

This two-stage approach ensures water is thoroughly purified both entering the dispenser and immediately before it is served.

Microplastics are plastic fragments smaller than 5 mm and they occur in tap water in two forms:

• Primary microplastics, e.g., from cosmetics, facial scrubs, and cleaning agents
• Secondary microplastics created by the breakdown of larger plastic products and car tires

Particles in water mainly originate from deposits that form in pipe systems. Chemically, they are a mixture of:

• Limescale and gypsum
• Silicates (sand)
• Corrosion residue (rust) from the pipes

Pressure surges or even normal water flow can dislodge and dissolve these deposits into the water.

Tap water normally contains no metals, but they can enter via rusting or aging pipes. Residential pipe systems may be made of:

• Galvanized steel
• Copper
• Stainless steel
• Brass
• Lead (in rare, typically older installations)

When water sits in these pipes, metal concentrations can occasionally exceed permitted limits.

Water treatment adds chlorine and chlorine compounds at the lowest possible concentration – ideally below the odor threshold. However, higher concentrations may be required for water transported over longer distances. Chlorine can also form compounds with organic substances that negatively affect taste and odor.

Organic impurities in water can take many forms:

• Industrial chemicals, e.g., solvents such as benzene
• Drug and pesticide residues
• Naturally occurring organic substances
• PFAS (synthetically produced chemicals, known as 'eternal chemicals'): a group of industrial substances that resist degradation and are now detectable in drinking water worldwide

These substances typically enter tap water via industrial emissions, agriculture, or general environmental pollution.

As rain falls through the atmosphere, it absorbs CO₂ and becomes slightly acidic. Once it reaches the ground, it dissolves minerals such as calcium carbonate, which increases the water's carbonate hardness. Excessive mineral content can affect the taste of drinks and lead to limescale deposits in appliances.

Tap water is clean by definition, but not sterile. It is treated to comply with microbiological limits. However, germs – such as bacteria and cysts – can still multiply as water flows through the pipe system, particularly where water is stagnant.

Pharmaceutical and hormone residues, along with their by-products, can enter the environment via wastewater and eventually reach tap water – though only in very small quantities. Water is commonly tested for naproxen, lindane, and estrone, as these substances occur particularly often.

Asbestos is a heat-resistant, fibrous silicate mineral once widely used as insulation, an anti-corrosion coating and a building material. It can enter water via pipe systems, including older asbestos-cement pipes (previously permitted) and asbestos-coated pipes.