Particles which remain in suspension in water are called suspended solids.
Suspended solids are particles which remain in suspension in water either due to the motion of the water or because the density of the particle is lighter or equal to the water. The suspended solid concentration is used as one of the indicators of water quality. All suspended solids can be removed from the water by filtration; however if the suspended solids have a density greater than water the particles can also be removed by sedimentation if the turbulence of the water is minimal.
Suspended solids can be of organic or inorganic origin. Organic material is substances that come from animal or plant sources. Organic substances always contain carbon, oxygen and hydrogen. Inorganic substances are on the other hand of mineral origin and do normally not contain carbon.
Suspended solids play an important role as pollutants both in terms of the organic or inorganic matter that constitutes them, but also by the pathogens that are carried on the surface of particles. Thus, the smaller the particle size, the greater the surface area per unit mass of particle – and therefore the greater the pathogenic load is likely to be carried.