Limit for drinking water: 5 ZF (formazine units or NTU)
- Visible water turbidity
- Impurities on the surface or settled at the bottom
- May contain harmful substances
- Provides shelter for bacteria
- Pollutes products, damages equipment, clogs pipes
Removing water turbidity
- Principle of solution: mechanical filtration
Turbidity represents the amount of undissolved substances carried by water. It may be inorganic (rust, sand, dust) or organic (clays, plant residues, overpopulated organisms – algae, cyanobacteria). Milky white cloudy water is usually caused by dissolved gases (most often oxygen), that quickly escape and do not pose a problem.
Suspended particles themselves settle at the bottom when the flow of water is slowing down. This forms sediments which may suddenly rise and get washed out with water (a typical situation after a water outage). Turbidity may originate directly from the water source, or it may come from corroded pipeline material, or it may form during water transport through chemical processes (precipitation).
To remove turbidity, mechanical filters are used. These may take the form of filter cartidges (cloth or other form of fibrous material), filter bed (sand, activated carbon and other granular materials) or screens and grids (plastic or metal; perforated or slotted). Turbidity is trapped on the surface of these filters while the water flows further. Filter cartridges need to be replaced over time. Other filters can be washed and reused. Most such filters offer the possibility of automatic washing.
