Water Quality Pollutant Determination Methods: Analytical Techniques, Standards and Applications

Water quality pollutant determination methods are essential analytical procedures used to identify and quantify physical, chemical, and biological contaminants in drinking water, surface water, groundwater, and wastewater. This technical guide summarizes the principal determination techniques—including titrimetry, spectrophotometry, atomic spectroscopy, and chromatography—along with applicable international and national standards such as ISO, ASTM, and GB. Whether for regulatory compliance, treatment process control, or environmental monitoring, understanding these methods helps laboratories select the correct procedure for each target pollutant.

Technical Overview

Water quality pollutant determination refers to the systematic measurement of contaminants in water matrices using validated physical, chemical, and biological analytical methods. These determinations are fundamental to public health protection, environmental regulation, industrial process control, and scientific research. Because different pollutants occur across an enormous concentration range—from percent levels down to parts per trillion—no single technique can cover all analytes, and method selection depends on the target compound, matrix type, required detection limit, and regulatory context.

Modern water analysis relies on a layered methodological framework. Classical wet-chemistry techniques such as titration, gravimetry, and colorimetry remain widely used for aggregate parameters like alkalinity, hardness, chemical oxygen demand (COD), and suspended solids. Instrumental methods—including UV-Vis spectrophotometry, atomic absorption spectroscopy (AAS), inductively coupled plasma optical emission spectrometry (ICP-OES), inductively coupled plasma mass spectrometry (ICP-MS), gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS), high performance liquid chromatography (HPLC), and ion chromatography (IC)—provide the sensitivity and selectivity needed for trace metals, nutrients, volatile and semi-volatile organics, and emerging contaminants such as per- and polyfluoroalkyl substances (PFAS).

Method harmonization is achieved through internationally recognized standards organizations. Key reference frameworks include ISO standards (for example, ISO 5815 for BOD, ISO 6060 for COD, ISO 11905 for total nitrogen, ISO 17294 for ICP-MS), ASTM International standards (for example, ASTM D1252 for COD, ASTM D1976 for trace elements by ICP-AES), and Chinese national standards (GB) such as GB 11893 for total phosphorus, GB 7479 for ammonia nitrogen, and the GB 5749 drinking water hygiene standard family. Government-published method documents, such as United States EPA reference methods, are also widely adopted globally. Accredited third-party laboratories typically operate these methods under ISO/IEC 17025 quality management systems, ensuring traceable calibration, method validation, and defensible reporting.

Testing Samples

Water pollutant determination covers a broad range of sample types, each with distinct sampling protocols, preservation requirements, and holding times. Representative matrices include:

Drinking Water and Treated Water

Treated tap water, bottled water, and water from purification systems are tested against hygiene standards such as GB 5749, the EU Drinking Water Directive, and WHO guidelines. Sampling typically uses sterilized or acid-washed containers, and microbiological samples must be analyzed within a few hours of collection to remain valid.

Surface Water

Rivers, lakes, reservoirs, and coastal waters are monitored to assess ecological status and compliance with environmental quality standards. Sampling depth, location, and flow conditions strongly influence representativeness, so depth-integrated or flow-weighted composite sampling is often required.

Groundwater

Water collected from monitoring wells and production wells is analyzed for naturally occurring constituents (iron, manganese, arsenic, fluoride) and anthropogenic contaminants (nitrate, chlorinated solvents, fuel hydrocarbons). Low-flow purging techniques minimize turbidity artifacts during sampling.

Municipal and Industrial Wastewater

Influent and effluent from wastewater treatment plants, as well as process water and discharge streams from industries such as electroplating, petrochemicals, pharmaceuticals, textiles, and food processing, are tested for discharge compliance. Composite samplers that collect flow-proportional 24-hour samples are commonly specified by discharge permits.

Seawater and Estuarine Water

High-salinity matrices require methods tolerant of dissolved salts, and higher detection limits are often accepted. Nutrients, heavy metals, and oil pollutants are the principal targets in marine monitoring programs.

Other Matrices

Leachate from landfills, stormwater runoff, recreational water, aquaculture water, cooling water, and boiler feed water are also routinely submitted for pollutant determination, each with matrix-specific method adaptations.

Testing Items

Determination programs are typically organized into parameter groups that mirror both regulatory limit tables and analytical technique families:

• Physical and aggregate parameters: pH, temperature, turbidity, color, odor, conductivity, total dissolved solids (TDS), total suspended solids (TSS), salinity, and oxidation-reduction potential (ORP).

• Nutrients and oxygen-demanding substances: chemical oxygen demand (COD), biochemical oxygen demand (BOD5), total organic carbon (TOC), ammonia nitrogen (NH3-N), nitrate (NO3-N), nitrite (NO2-N), total nitrogen (TN), total phosphorus (TP), and dissolved oxygen (DO).

• Heavy metals and metalloids: lead, cadmium, mercury, arsenic, hexavalent chromium, total chromium, copper, zinc, nickel, iron, manganese, aluminum, selenium, antimony, beryllium, thallium, and barium.

• Organic pollutants: volatile organic compounds (VOCs) such as benzene, toluene, ethylbenzene, and xylenes (BTEX) and trihalomethanes; semi-volatile organics including polycyclic aromatic hydrocarbons (PAHs) and phthalates; phenolic compounds; petroleum hydrocarbons and oil and grease; anionic and nonionic surfactants; pesticides; and polychlorinated biphenyls (PCBs).

• Microbiological indicators: total coliforms, thermotolerant (fecal) coliforms, Escherichia coli, total heterotrophic plate count, Enterococci, and fecal streptococci.

• Emerging contaminants: PFAS compounds, endocrine-disrupting chemicals, pharmaceutical residues, personal care product ingredients, disinfection by-products such as haloacetic acids, and microplastics.

• Radioactive and other special parameters: gross alpha and gross beta activity, radon, uranium, free chlorine and residual disinfectants, cyanide, fluoride, and sulfide.

Testing Methods

Determination techniques are matched to analyte class, concentration range, and required turnaround. The following methods represent the core toolkit of accredited water testing laboratories:

Titrimetric and Gravimetric Methods

Classical wet-chemistry determinations remain the reference procedures for many aggregate parameters. COD is determined by dichromate reflux titration or the fast digestion spectrophotometric variant; alkalinity and chloride by acid-base and argentometric titration; water hardness by EDTA complexometric titration; and TSS and oil and grease by filtration and solvent-extraction gravimetry, respectively. These methods are robust, inexpensive, and traceable to standards such as ISO 6060 and ASTM D1252.

UV-Vis Spectrophotometry and Colorimetry

Molecular absorption spectrophotometry is the workhorse for nutrients and specific ions. Ammonia nitrogen is measured with Nessler's reagent or the salicylate method; total phosphorus by ammonium molybdate spectrophotometry after persulfate digestion (GB 11893); hexavalent chromium by the 1,5-diphenylcarbohydrazide method; and cyanide, fluoride, sulfide, anionic surfactants, and residual chlorine by dedicated colorimetric or flow-injection procedures. Automated segmented-flow and discrete analyzers allow high-throughput determination of these parameters.

Atomic Absorption and ICP Techniques for Metals

Flame atomic absorption spectrometry (FAAS) suits metals at mg/L levels, while graphite furnace AAS extends detection to µg/L levels for elements such as lead, cadmium, and arsenic. Cold vapor AAS remains the standard approach for mercury. ICP-OES enables simultaneous multi-element determination, and ICP-MS provides ultra-trace multi-element capability with detection limits at ng/L levels, following standards such as ISO 17294 and the EPA 200.8 method family. Hydride generation techniques improve sensitivity for arsenic, selenium, and antimony, and speciation analysis couples HPLC with ICP-MS to distinguish, for example, trivalent from hexavalent chromium.

Gas Chromatography and GC-MS for Organic Pollutants

Volatile organics are determined by purge-and-trap or headspace GC-MS, covering BTEX, chlorinated solvents, and trihalomethanes. Semi-volatiles such as PAHs, phthalates, nitrosamines, and pesticides are extracted by liquid-liquid extraction or solid-phase extraction and determined by GC-MS or GC with selective detectors (ECD, FPD, NPD). Oil and grease and total petroleum hydrocarbons are quantified by infrared spectrometry or gravimetry after extraction, while mineral oil hydrocarbons can be fractionated by GC.

Liquid Chromatography and Hyphenated Techniques

HPLC with UV, fluorescence, or diode-array detection determines thermally labile compounds such as certain pesticides, phenols, and azo dyes. HPLC-MS/MS has become the definitive technique for PFAS, pharmaceuticals, endocrine disruptors, cyanotoxins such as microcystins, and haloacetic acids, delivering the low-ng/L detection limits demanded by modern drinking water regulation.

Ion Chromatography

Ion chromatography simultaneously determines common anions (fluoride, chloride, nitrite, bromide, nitrate, phosphate, sulfate) and cations (lithium, sodium, ammonium, potassium, calcium, magnesium) with minimal sample preparation, and supports bromate and chlorite determination in ozonated and chlorinated waters.

Biochemical and Microbiological Methods

BOD5 is determined by the dilution-and-incubation method (ISO 5815) or by respirometric and manometric alternatives. Total coliforms, E. coli, and Enterococci are enumerated by membrane filtration and incubation on selective media or by defined-substrate enzyme methods such as Colilert; enzyme-substrate and quantitative PCR methods shorten turnaround to same-day reporting for certain targets. Cytotoxicity and bioassay screening complement chemical analysis for holistic quality assessment.

Continuous and Field Measurement

Online analyzers and multi-parameter probes provide continuous determination of pH, DO, turbidity, conductivity, ammonia, nitrate, COD via UV254 correlation, and residual chlorine at treatment plants and discharge points, enabling real-time process control and early-warning monitoring.

Applications

Determination of water pollutants supports decision-making across many sectors:

• Regulatory compliance monitoring of industrial and municipal discharges against effluent limits defined in discharge permits and national standards such as GB 8978.

• Drinking water quality verification for water utilities, bottled water producers, and building water systems, including lead and copper surveys and disinfection by-product surveillance.

• Environmental status assessment of rivers, lakes, groundwater aquifers, and coastal zones under surface water and groundwater quality classification standards.

• Wastewater treatment process optimization, including aeration control, nutrient removal monitoring, and effluent polishing verification.

• Environmental impact assessments, pollution incident investigations, and forensic source tracking using contaminant fingerprinting.

• Soil and groundwater remediation verification, where trend monitoring demonstrates the effectiveness of cleanup technologies.

• Industrial water cycle management in power generation, semiconductor fabrication, pharmaceutical manufacturing, and food and beverage production, where ultrapure and process water specifications demand trace-level determinations.

• Research applications, including emerging contaminant occurrence studies, ecotoxicology support, and development of new treatment technologies.

FAQ

What is the difference between COD and BOD determination?

COD measures the oxygen equivalent of chemically oxidizable matter using a strong oxidant (typically dichromate), capturing both biodegradable and non-biodegradable organics within hours. BOD5 measures the oxygen consumed by microorganisms during five days of incubation, reflecting only the biodegradable fraction. COD is faster and more reproducible; BOD better represents the biological impact on receiving waters.

Which method is best for trace heavy metals in water?

ICP-MS is generally preferred for multi-element ultra-trace determination because it offers ng/L-level detection limits and wide linear range. Graphite furnace AAS is a robust single-element alternative, while flame AAS suffices for higher concentrations such as iron and manganese in well water. Mercury is best determined by cold vapor techniques.

Why must water samples be preserved before analysis?

Preservation retards biological degradation, precipitation, adsorption to container walls, and volatilization losses between sampling and analysis. Common measures include acidification to pH below 2 with nitric acid for metals, refrigeration at 4 °C for nutrients and organics, chemical fixation for dissolved oxygen, and the addition of sodium thiosulfate to quench residual chlorine in microbiological samples.

How are emerging contaminants such as PFAS determined?

PFAS compounds are determined by solid-phase extraction followed by HPLC-MS/MS using isotope-dilution quantification, achieving sub-ng/L detection limits. Strict sampling protocols, avoiding fluoropolymer-containing equipment, are essential to prevent cross-contamination, and standardized methods from recognized bodies are applied to ensure comparability.

Can a single analysis cover all pollutants in a water sample?

No. Different pollutant classes require different sample preparation, instrumentation, and detection principles. A typical comprehensive assessment combines physical-instrumental panels, ICP-MS metal scans, chromatographic organic screens, and microbiological testing, with the scope tailored to the applicable standard or permit.

How do laboratories ensure the reliability of determination results?

Accredited third-party laboratories operate under ISO/IEC 17025 systems, employing certified reference materials, calibration standards traceable to national metrology institutes, method validation with documented detection limits and precision, internal quality controls, duplicate and spiked samples, proficiency testing participation, and rigorous data review before reporting.