How Does a City Purify Its Water?
Water in its natural state is often dirty, and usually must be purified to be safe for consumption. After water is drawn from a lake or reservoir, it is piped to a water treatment plant. There, certain chemicals are added that cause dirt and other impurities to lump together.
The water then goes into a big settling tank where the lumps of dirt settle to the bottom. The water is then filtered to remove any remaining impurities and to make it sparkling clear. Finally, very small amounts of chlorine are added to the water to kill any harmful germs.
Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids and gases from contaminated water.
Most water is disinfected for human consumption, but water purification may also be designed for a variety of other purposes, including fulfilling the requirements of medical, pharmacological, chemical and industrial applications.
The methods used include physical processes such as filtration, sedimentation, and distillation; biological processes such as slow sand filters or biologically active carbon; chemical processes such as flocculation and chlorination and the use of electromagnetic radiation such as ultraviolet light.
Purifying water may reduce the concentration of particulate matter including suspended particles, parasites, bacteria, algae, viruses, fungi, as well as reducing the amount of a range of dissolved and particulate material derived from the surfaces that come from runoff due to rain.
The standards for drinking water quality are typically set by governments or by international standards. These standards usually include minimum and maximum concentrations of contaminants, depending on the intended purpose of water use.