Potable versus pure water and treatment reasons
Using resources • Earth's resources and potable water
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Definition of pure water
Pure water consists solely of H2O molecules with no dissolved salts, gases, particles or microorganisms. Laboratory-grade pure water reaches this state by processes such as distillation or deionisation. Practical limitation: absolute chemical purity is difficult to maintain in stored or distributed water because exposure to air causes dissolved gases and contact with containers introduces trace ions.
Definition of potable water
Potable water contains water that meets health-based and aesthetic standards for human consumption. Potable water includes some dissolved ions (for taste and to prevent pipe corrosion) but keeps harmful chemicals and biological contaminants below regulatory limits. Limiting factors: regional standards vary and treatment focuses on reducing risk rather than eliminating every detectable trace of a substance.
Screening and coarse removal
Screening causes large objects and coarse solids to be prevented from entering the treatment system. Effect: reduced clogging and reduced load on downstream processes such as sedimentation and filtration. Screening protects mechanical equipment and improves overall treatment efficiency.
Sedimentation and coagulation
Coagulation adds chemicals that cause fine suspended particles to clump, and sedimentation allows these flocs to settle out by gravity. Cause→effect: destabilised particles aggregate, increasing settling rate; settled solids reduce turbidity and lower microbial shelters, making disinfection more effective. Limiting factors: very small colloidal particles require effective coagulant dosing and contact time.
Filtration and removal of particulates
Filtration passes water through sand, gravel or membrane media to remove remaining suspended solids and some microbes. Cause→effect: physical straining and adsorption reduce turbidity and trapped particles, producing clearer water and protecting disinfection stages. Limiting factors: filter pore size determines which particles and organisms are removed; membrane filters remove smaller solutes but require more energy and maintenance.
Disinfection and microbial control
Disinfection uses chemical agents (such as chlorine) or physical methods (such as ultraviolet light) to inactivate pathogenic microorganisms. Cause→effect: inactivation of bacteria, viruses and protozoa reduces the risk of waterborne disease. Limiting factors: some pathogens show resistance to certain disinfectants and chemical by-products can form when disinfectants react with organic matter.
Chemical adjustments and removal of dissolved ions
Treatment adjusts pH, hardness and specific ion concentrations by processes such as lime addition, ion exchange, reverse osmosis or deionisation. Cause→effect: pH adjustment prevents corrosion and improves coagulation; ion removal reduces hardness and toxic ions, improving health and appliance lifespan. Limiting factors: complete removal of all dissolved ions requires energy-intensive processes and may remove beneficial minerals.
Desalination and special treatments
Desalination processes (reverse osmosis, distillation) remove salts from seawater or brackish sources to produce potable water. Cause→effect: high-pressure membranes or phase-change separation separate water from dissolved salts, producing water that meets potable standards. Limiting factors: high energy use, brine disposal and cost limit desalination to regions with scarce freshwater supplies.
Key notes
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