Water Quality Testing: Core Parameters & Authoritative Methods (2025)

Water quality testing is a core technical means for assessing water body safety, identifying pollution hazards, and ensuring water consumption health. Different testing parameters correspond to distinct characteristics of water bodies, and the selection of their detection methods directly affects data accuracy. This article systematically sorts out 20 core testing parameters across five categories, covering detection methods, reference standards, indicator significance, and applicable scenarios, providing a comprehensive reference for water quality testing practitioners, environmental protection personnel, and professionals in related industries.

I. Comprehensive Physicochemical Indicators: The "Intuitive Ruler" for Basic Water Body Properties

Comprehensive physicochemical indicators directly reflect the fundamental state of water bodies and serve as the "first step" in water quality testing. They are mainly used to judge basic characteristics such as water pH, cleanliness, and ion content. The core parameters and key testing points are as follows:

1. pH Value

Authoritative Detection Method: Glass electrode method; Reference Standard: GB/T 6920-1986, HJ 1147-2020; Indicator Significance & Applicable Scenarios: Reflects the acidity and alkalinity of water bodies, affecting the solubility of chemical substances and the activity of microorganisms. Applicable to all water bodies, especially industrial wastewater (e.g., abnormal pH of electroplating wastewater can easily cause heavy metal precipitation) and drinking water (standard pH range: 6.5-8.5).

2. Dissolved Oxygen (DO)

Authoritative Detection Method: Electrochemical probe method (on-site rapid detection), iodometric method (laboratory precise detection); Reference Standard: GB 7489-1987, HJ 506—2009, HJ 925-2017; Indicator Significance & Applicable Scenarios: Characterizes the self-purification capacity of water bodies and the living environment of aquatic organisms. When DO is lower than 2mg/L, water bodies are prone to blackening and odor. Applicable to the detection of surface water, sewage treatment plant effluent, aquaculture water, and other scenarios.

3. Turbidity (NTU)

Authoritative Detection Method: Nephelometry, spectrophotometry; Reference Standard: GB 13200-91; Indicator Significance & Applicable Scenarios: Reflects the content of suspended particles in water, serving as a core indicator of sensory properties. The turbidity of drinking water must be ≤1 NTU, and that of sewage treatment plant effluent must be ≤5 NTU. Applicable to the detection of drinking water, secondary water supply, surface water, and other scenarios.

4. Color

Authoritative Detection Method: Platinum-cobalt colorimetric method, dilution multiple method; Reference Standard: GB 11903-89; Indicator Significance & Applicable Scenarios: Reflects the depth of water color, caused by soluble organic matter, metal ions, etc., and is an important indicator of sensory properties. The color of drinking water must be ≤15 degrees. The color of industrial wastewater (e.g., printing and dyeing, papermaking wastewater) often exceeds the standard. Applicable to the detection of drinking water, surface water, industrial wastewater, and other scenarios.

5. Conductivity

Authoritative Detection Method: Electrode method; Reference Standard: HJ/T 97-2003; Indicator Significance & Applicable Scenarios: Indirectly measures the total ion concentration in water, reflecting the mineralization degree or pollution level of water bodies. Pure water has extremely low conductivity, while industrial wastewater has significantly increased conductivity due to high salt content. Applicable to water quality type identification, pollution source tracing, and other scenarios.

6. Suspended Solids (SS)

Authoritative Detection Method: Gravimetric method; Reference Standard: GB 11901-89; Indicator Significance & Applicable Scenarios: Refers to solid particles that cannot pass through a filter, serving as a key indicator for sewage treatment discharge control. The SS content of sewage treatment plant influent can reach several hundred mg/L, and that of effluent must be controlled within 10-30 mg/L. Applicable to the detection of industrial wastewater, domestic sewage, and other scenarios.

7. Total Solids (TS)

Authoritative Detection Method: Gravimetric method (drying and weighing at 103-105℃); Reference Standard: General detection specifications; Indicator Significance & Applicable Scenarios: Includes the total amount of soluble and suspended solids, reflecting the total solid load of water bodies. Applicable to industrial wastewater discharge, seawater desalination, groundwater mineralization assessment, and other scenarios.

II. Comprehensive Indicators of Organic Pollutants: The "Quantitative Core" for Organic Pollution in Water Bodies

Comprehensive indicators of organic pollutants are used to assess the overall pollution level of organic matter in water bodies. They cannot distinguish specific pollutant types but can quickly judge the severity of pollution, serving as key indicators for sewage treatment and pollution source monitoring. The core parameters and key testing points are as follows:

1. Chemical Oxygen Demand (COD)

Authoritative Detection Method: Dichromate method (CODCr); Reference Standard: HJ 828—2017 (Replacing GB 11914-89); Indicator Significance & Applicable Scenarios: Characterizes the total amount of organic matter that can be decomposed by strong oxidants, serving as a core indicator of sewage pollution degree. The COD of domestic sewage is about 300-500 mg/L, and that of industrial wastewater can reach several thousand mg/L. Applicable to all water body pollution assessment scenarios.

2. Permanganate Index (CODMn)

Authoritative Detection Method: Permanganate method (acidic/alkaline); Reference Standard: GB 11892-89; Indicator Significance & Applicable Scenarios: The oxidant has weak oxidizing properties and only detects easily oxidizable organic matter. Applicable to slightly polluted surface water, drinking water, and source water, often used as a reference indicator for water quality cleanliness.

3. Five-Day Biochemical Oxygen Demand (BOD₅)

Authoritative Detection Method: Dilution and seeding method; Reference Standard: HJ 505—2009; Indicator Significance & Applicable Scenarios: Characterizes the content of biodegradable organic matter. A BOD₅/COD ratio > 0.3 indicates good biodegradability of wastewater. Applicable to sewage treatment process selection, biochemical treatment effect assessment, and other scenarios.

III. Nutrient Salt Indicators: The "Key Inducer" for Eutrophication of Water Bodies

Nutrient salt indicators mainly include nitrogen and phosphorus compounds, which are the core factors leading to water eutrophication (cyanobacteria bloom, water bloom). They are also the focus of detection for surface water, landscape water, and drinking water sources. The core parameters and key testing points are as follows:

1. Total Nitrogen (TN)

Authoritative Detection Method: Alkaline potassium persulfate digestion-ultraviolet spectrophotometry; Reference Standard: HJ 636-2012; Indicator Significance & Applicable Scenarios: Includes all forms of nitrogen such as organic nitrogen, ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen, reflecting the total nitrogen load of water bodies. Surface water with TN > 1.0 mg/L is prone to eutrophication. Applicable to the detection of lakes, reservoirs, sewage treatment plant effluent, and other scenarios.

2. Ammonia Nitrogen (NH₃-N)

Authoritative Detection Method: Nessler's reagent spectrophotometry; Reference Standard: HJ 535-2009; Indicator Significance & Applicable Scenarios: Exists in the form of free ammonia and ammonium ions, toxic to aquatic organisms, and is a core monitoring indicator for sewage nitrification treatment. The ammonia nitrogen content of drinking water must be ≤ 0.5 mg/L. Applicable to the detection of sewage, surface water, drinking water, and other scenarios.

3. Nitrate Nitrogen (NO₃⁻-N)

Authoritative Detection Method: Ultraviolet spectrophotometry, ion chromatography; Reference Standard: HJ/T 346-2007; Indicator Significance & Applicable Scenarios: The final product of nitrification. Excessively high content in drinking water can easily cause methemoglobinemia in infants. Applicable to the detection of drinking water, groundwater, farmland drainage, and other scenarios.

4. Nitrite Nitrogen (NO₂⁻-N)

Authoritative Detection Method: N-(1-Naphthyl)-ethylenediamine spectrophotometry; Reference Standard: GB 7493-87; Indicator Significance & Applicable Scenarios: An intermediate product of the nitrification process, unstable and toxic, serving as an "early warning indicator" for water quality deterioration. Applicable to sewage treatment process monitoring, surface water pollution investigation, and other scenarios.

5. Total Phosphorus (TP)

Authoritative Detection Method: Ammonium molybdate spectrophotometry; Reference Standard: GB 11893-89; Indicator Significance & Applicable Scenarios: Includes all forms of phosphorus, and together with total nitrogen, determines the degree of water eutrophication. Surface water with TP > 0.02 mg/L has the risk of eutrophication. Applicable to the detection of lakes, reservoirs, sewage treatment plant effluent, and other scenarios.

IV. Heavy Metals and Specific Inorganic Pollutants: The "Invisible Killer" of Water Body Toxicity Risks

This category of indicators involves toxic and harmful pollutants. Some heavy metals (such as mercury, cadmium, and lead) have cumulative toxicity, and are key detection items for drinking water safety, industrial wastewater discharge, and soil pollution source tracing. The core parameters and key testing points are as follows:

1. Heavy Metals (Arsenic, Cadmium, Chromium, Copper, Lead, Mercury, Zinc, etc.)

Authoritative Detection Method: Atomic Absorption Spectroscopy (AAS), Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES), Inductively Coupled Plasma Mass Spectrometry (ICP-MS); Reference Standard: GB 7475-87, HJ/T 341─2007; Indicator Significance & Applicable Scenarios: High precision for trace/microtrace detection. AAS is suitable for single-element detection, while ICP-OES/ICP-MS is suitable for simultaneous multi-element detection. Applicable to the detection of drinking water, industrial wastewater (electroplating, metallurgical industries), soil leachate, and other scenarios.

2. Fluoride (F⁻)

Authoritative Detection Method: Ion-selective electrode method; Reference Standard: GB 7484-87; Indicator Significance & Applicable Scenarios: The limit of fluoride in drinking water is 1.0 mg/L. Too low a content can easily cause dental caries, while too high a content can lead to dental fluorosis. Applicable to the detection of drinking water, groundwater (high-fluoride areas), fluorochemical industry wastewater, and other scenarios.

3. Cyanide (CN⁻)

Authoritative Detection Method: Iso-nicotinic acid-pyrazolone spectrophotometry; Reference Standard: General detection specifications; Indicator Significance & Applicable Scenarios: A highly toxic pollutant, mainly derived from wastewater of electroplating, metallurgical, and coking industries. It must be strictly controlled in drinking water. Applicable to industrial wastewater discharge, surface water emergency monitoring, and other scenarios.

4. Residual Chlorine

Authoritative Detection Method: N,N-Diethyl-p-phenylenediamine (DPD) spectrophotometry; Reference Standard: General detection specifications; Indicator Significance & Applicable Scenarios: Reflects the disinfection effect. The residual chlorine in the tap water at the end of the pipe network must be ≥ 0.05 mg/L, and too high a content affects the taste. Applicable to the detection of disinfection effects of drinking water, secondary water supply, sewage treatment plant effluent, and other scenarios.

5. Total Chlorine

Authoritative Detection Method: N,N-Diethyl-p-phenylenediamine (DPD) spectrophotometry; Reference Standard: GB/T 5750.11-2006, HJ 586-2010; Indicator Significance & Applicable Scenarios: Refers to the sum of free chlorine and combined chlorine in water. Combined chlorine (such as chloramine) has weak disinfection effect but high stability. Applicable to drinking water disinfection process optimization and pipe network water quality stability assessment to ensure continuous and effective disinfection.

6. Chlorine Dioxide (ClO₂)

Authoritative Detection Method: N,N-Diethyl-p-phenylenediamine (DPD) spectrophotometry, iodometric method; Reference Standard: HJ 551-2016, GB/T 5750.11-2006; Indicator Significance & Applicable Scenarios: A high-efficiency disinfectant whose disinfection effect is not affected by pH and produces few by-products. The residual amount of chlorine dioxide in drinking water must be ≤ 0.8 mg/L. Applicable to the detection of disinfection effects of drinking water and food processing water, especially suitable for disinfection scenarios of water bodies with high pH or containing ammonia nitrogen.

V. Microbiological Indicators: The "Ultimate Line of Defense" for Water Body Sanitary Safety

Microbiological indicators are used to judge whether water bodies are contaminated by feces or pathogenic bacteria. They are core sanitary indicators for water bodies in direct contact with humans, such as drinking water, swimming pool water, and landscape water. The core parameters and key testing points are as follows:

1. Total Coliforms

Authoritative Detection Method: Multiple-tube fermentation method, membrane filtration method; Reference Standard: HJ 347.2-2018; Indicator Significance & Applicable Scenarios: Indicator microorganisms for fecal contamination, which must not be detected in drinking water. Applicable to the sanitary assessment of drinking water, surface water, sewage treatment plant effluent, and other scenarios.

2. Escherichia coli (E.coli)

Authoritative Detection Method: Enzyme substrate method (such as Colilert™ reagent); Reference Standard: HJ 1001-2018; Indicator Significance & Applicable Scenarios: Specifically indicates recent fecal contamination, more accurate than total coliforms, and must not be detected in drinking water. Applicable to the detection of drinking water, food processing water, and other scenarios.

VI. Key Testing Reminders: Core Principles for Ensuring Data Accuracy

1. Standard Priority: All tests must strictly follow the corresponding national standards or industry standards, and priority shall be given to the current valid standards (e.g., HJ 828—2017 replaces the original GB 11914-89);

2. Method Adaptation: For on-site rapid detection, electrochemical probe method and portable spectrophotometry are preferred; for laboratory precise detection, gravimetric method, atomic absorption spectroscopy, and other methods are selected;

3. Quality Control: For each batch of tests, blank experiments, parallel sample tests, and spiked recovery experiments must be conducted to ensure data accuracy and repeatability;

4. Sample Preservation: Different indicators have different sample preservation conditions (e.g., ammonia nitrogen samples need to be refrigerated and tested within 24 hours) to avoid data distortion caused by sample deterioration.

Water quality testing is a systematic project, and appropriate parameters and methods should be selected according to the testing purpose and water body type. The core parameters and methods sorted out in this article cover most water quality testing scenarios. Practitioners can flexibly apply them in combination with actual needs. At the same time, they need to pay attention to the update dynamics of standards to ensure the standardization and authority of testing work.

---

---