Hydrophilicity describes the property of a substance to attract water or to dissolve in water. Hydrophilic molecules have polar groups, such as hydroxyl (-OH), amine (-NH₂) or carboxyl groups (-COOH), which can form hydrogen bonds with water molecules. This property distinguishes them from hydrophobic molecules, which repel water and dissolve in non-polar solvents instead.

Technical background
Hydrophilicity is crucial in water treatment, as many filter and membrane systems are based on this property. Hydrophilic materials such as cellulose acetate or polyvinyl alcohol are often used in membranes as they have a high wettability and promote water flow. In adsorption processes, hydrophilic surfaces help to effectively bind dissolved polar substances.

Applications in practice

1. Membrane filtration
   Hydrophilic membranes are particularly effective in ultrafiltration and nanofiltration systems. They offer high permeability and a lower susceptibility to fouling by organic substances, as they promote a natural rejection of hydrophobic particles.

2. Chemical treatment
   In industrial wastewater treatment plants, hydrophilic chemicals are used to bind and separate organic substances and pollutants in the water. Typical examples are hydrophilic flocculants, which efficiently remove dissolved solids.

3. Coatings and filter materials
   Hydrophilic coatings on filter materials improve water absorption and prevent the formation of hydrophobic barriers, which increases filtration efficiency.