Water Quality

A document outlining the definition of water quality, assessment indicators, pollution sources, management technologies, and regulatory and technology trends in 2024–2025.

Water Quality

Overview

Water quality (水質, Water Quality) is a concept that comprehensively represents the physical, chemical, and biological characteristics of water, and is a core environmental indicator directly linked to drinking water use, industrial and agricultural water, and aquatic ecosystem health. Water quality is assessed not only by pollutant concentrations but also by various items such as water temperature, turbidity, dissolved oxygen (DO), pH, nutrients, heavy metals, and microorganisms, and is managed through national environmental standards and recommendations from international organizations such as WHO and the EU. With climate change, urbanization, and the emergence of emerging contaminants, water quality management is expanding beyond simple pollution treatment to agendas of resource circulation and sustainability.

Main Content

Definition and Assessment Indicators of Water Quality

Water quality is largely assessed by dividing it into physical, chemical, biological, and ecological indicators.

  • Physical indicators: water temperature, turbidity, color, suspended solids (SS), electrical conductivity, odor and taste
  • Chemical indicators: pH, dissolved oxygen (DO), biochemical oxygen demand (BOD), chemical oxygen demand (COD), total organic carbon (TOC), total nitrogen (T-N) and total phosphorus (T-P), heavy metals (lead, mercury, cadmium, arsenic), pesticide residues
  • Biological indicators: coliform bacteria and fecal indicator bacteria, total bacterial count, chlorophyll-a (algal biomass)
  • Ecological health indicators: benthic macroinvertebrate index (BMI), fish community index, riparian vegetation index

BOD and COD are representative indicators of organic pollution, and recently there is an expanding shift to TOC, which enables rapid measurement and high reproducibility. Nutrient concentrations are used as key predictive variables for eutrophication and algal bloom occurrence.

Water Quality Standards and Legal Regulations

Korea establishes water quality and aquatic ecosystem environmental standards for rivers and lakes in stages from very good (Ia) to very bad (VI) under the Water Environment Conservation Act, and prescribes drinking water quality standards for dozens of items under the Drinking Water Management Act. Industrial wastewater and public sewerage are managed by individual effluent allowance standards and effluent water quality standards.

Internationally, the US Clean Water Act and Safe Drinking Water Act, the EU Water Framework Directive (2000/60/EC) and Drinking Water Directive, and WHO drinking water quality guidelines are representative. The International Organization for Standardization (ISO) provides water quality test methods and water service management standards (such as ISO 24512).

Main Causes of Water Pollution

  • Point sources: industrial wastewater, wastewater treatment plant effluent, livestock wastewater, landfill leachate
  • Nonpoint sources: runoff of fertilizers and pesticides from agricultural land, stormwater runoff from urban impervious surfaces, atmospheric deposition, construction site sediment
  • Emerging contaminants: microplastics, pharmaceutical residues (PPCPs), per- and polyfluoroalkyl substances (PFAS), personal care products, antibiotic resistance genes
  • Complex pollution: algal blooms and red tides caused by eutrophication, acid mine drainage (AMD), saltwater intrusion, spread of groundwater contamination

Measurement and Monitoring

Water quality measurement is fundamentally based on sample collection and laboratory analysis, but real-time monitoring through automatic water quality monitoring networks (TMS) and IoT sensors is becoming common. Satellite remote sensing observes algal distribution in lakes and coastal areas over wide areas, and drones and unmanned vessels survey inaccessible points. Biota monitoring based on environmental DNA (eDNA), biological early warning systems, and water system digital twin models are also being introduced into practice.

Water Quality Management and Purification Technologies

  • Advanced sewage and wastewater treatment: nitrogen and phosphate removal such as membrane separation activated sludge (MBR) and the A2O process, ozone oxidation, activated carbon adsorption
  • Drinking water treatment: combining basic processes of coagulation, sedimentation, and filtration with ozone-activated carbon advanced water treatment and membrane filtration (UF/RO)
  • Contaminated groundwater and soil remediation: permeable reactive barriers (PRB), pump-and-treat, bioremediation
  • Nature-based solutions: constructed wetlands, river ecological restoration, low impact development (LID), vegetated buffer strips
  • Nonpoint source pollution reduction: retention and infiltration facilities, constructed wetlands, first flush treatment facilities

Recent Trends

The biggest change in the water quality field in 2024–2025 is the full-scale regulation of emerging contaminants. Drinking water standards for PFAS (per- and polyfluoroalkyl substances) have been strengthened, centered on the EU and the US, and Korea is also considering expanding PFAS management items and strengthening monitoring. For microplastics, establishing standardized measurement methods in wastewater treatment plant effluent and drinking water sources is under discussion, and the EU is introducing monitoring obligations in its Drinking Water Directive in stages.

Digital transformation is also notable. AI-based algal bloom prediction models, real-time water quality sensor networks, satellite-drone integrated monitoring, and water system digital twins are being pilot-operated by local governments and research institutions. In terms of responding to climate change, increased nonpoint source pollution runoff due to droughts and heavy rainfall, prolonged algal blooms due to rising water temperatures, and saltwater intrusion have emerged as new management challenges. Along with this, wastewater reuse and direct and indirect potable reuse (DPR/IPR) are spreading as measures to respond to water scarcity, and there is also a growing movement to integrate monitoring of antibiotic-resistant bacteria (AMR) in the water environment from a One Health perspective.

Related Topics

  • [[Water Resources]]
  • [[Water Pollution]]
  • [[Drinking Water Supply]]
  • [[Environmental Standards]]
  • [[Microplastics]]
  • [[Climate Change]]
  • [[PFAS]]