Sources and treatment of potable water
Using resources • Earth's resources and potable water
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Definition of potable water and source types
Potable water meets chemical and microbiological standards for human consumption. Groundwater is water stored underground in rock or sediment pores. Seawater is ocean water with about 35 g of dissolved salts per litre. Wastewater originates from homes, industry and storm runoff and contains organic pollutants, microbes and suspended solids. Source type determines typical contaminants and the subsequent treatment strategy.
Typical contaminants and limiting factors by source
Groundwater typically contains minerals such as calcium and magnesium (hardness), iron, and sometimes dissolved gases or low levels of microbes. Limiting factors include mineral concentration and local geology. Seawater contains very high concentrations of dissolved salts and often organic matter near coasts; the limiting factor is salt concentration, which requires energy-intensive separation. Wastewater contains organic carbon, nutrients (nitrate, phosphate), pathogens and variable industrial chemicals; the limiting factors include pathogen load, toxic chemicals and the need for advanced biological or chemical treatment.
Treatment steps for groundwater
Groundwater treatment focuses on physical and chemical removal of dissolved minerals and any particulates. Common steps include aeration to remove dissolved gases and oxidize iron, filtration to remove suspended solids, and softening or ion exchange to reduce hardness. Disinfection (chlorination or UV) follows to ensure microbiological safety if necessary. Cause → effect: aeration oxidizes dissolved iron → iron precipitates → filtration removes precipitates; disinfection inactivates microbes → water becomes microbiologically safe.
Treatment steps for seawater (desalination)
Desalination removes dissolved salts to produce potable water. Two common methods include thermal distillation and membrane processes. Thermal distillation heats seawater to produce vapor → vapor condenses as fresh water, leaving salts behind. Reverse osmosis forces seawater through semipermeable membranes under high pressure → salts remain in the concentrate. Pre-treatment removes particulates and organic matter to protect membranes or heat exchangers, and post-treatment adjusts pH and adds minerals for taste and stability.
Treatment steps for wastewater (sewage treatment and advanced purification)
Wastewater treatment uses mechanical, biological and chemical stages. Primary treatment removes large solids by screening and sedimentation. Secondary biological treatment uses microbes to break down organic matter → biological solids settle out. Tertiary treatment removes nutrients, remaining suspended solids and specific contaminants by filtration, chemical precipitation or advanced oxidation. Disinfection (chlorination, UV, ozonation) inactivates pathogens. Advanced purification for potable reuse may add membrane filtration and reverse osmosis followed by advanced oxidation to remove trace contaminants.
Relative ease of obtaining potable water from each source
Groundwater is generally easier to treat because salt concentrations are low and treatment often requires simple filtration, softening and disinfection, resulting in lower energy needs. Seawater is hardest to treat because desalination demands high energy and corrosion-resistant infrastructure. Wastewater treatment to potable standard varies: conventional treatment to remove solids and organics is well established, but producing potable-quality water requires advanced multi-stage purification and robust monitoring to remove pathogens and trace chemicals, increasing complexity and cost.
Key notes
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