Dissolved and suspended particles are present in most of natural waters. These suspended materials mostly arise from land erosion, the dissolution of minerals and the decay of vegetation and from several domestic and industrial waste discharges. Such material may include suspended, dissolved organic and/or inorganic matter, as well as several biological organisms, such as bacteria, algae or viruses. This material has to be removed, as it causes deterioration of water quality by reducing the clarity (e.g. causing turbidity or colour), and eventually carrying pathogenic organisms or toxic compounds, adsorbed on their surfaces