Reclaimed water quality testing is essential for verifying that recycled wastewater meets national safety and performance standards before reuse in urban, industrial, agricultural, and environmental applications. This technical guide explains the applicable standards, sampling procedures, key testing parameters, analytical methods, and practical considerations for professional reclaimed water quality assessment. Whether you operate a water reclamation plant, industrial recycling system, or building greywater system, understanding these testing requirements ensures regulatory compliance and safe operation.
Technical Overview
Reclaimed water, also known as recycled water or reused water, refers to municipal or industrial wastewater that has been treated to a quality level suitable for beneficial non-potable reuse rather than direct discharge. Because reclaimed water is used for purposes such as landscape irrigation, industrial cooling, toilet flushing, road cleaning, and ecological replenishment, its quality directly affects public health, equipment longevity, product quality, and environmental safety. Systematic quality testing is therefore a mandatory component of every water reclamation project.
In China, reclaimed water quality is governed by a framework of national standards, each corresponding to a specific reuse category:
- GB/T 18920 – Water quality standard for urban miscellaneous water use (toilet flushing, vehicle washing, road cleaning, urban greening, construction)
- GB/T 18921 – Water quality standard for scenic environment use (ornamental and recreational water bodies, wetland replenishment)
- GB/T 19923 – Water quality standard for industrial use (cooling water, boiler makeup water, process water)
- GB 20922 – Water quality standard for farmland irrigation reuse
- GB/T 19772 – Water quality standard for groundwater recharge
Professional testing is performed by laboratories accredited under CMA (China Metrology Accreditation) and CNAS (China National Accreditation Service), and results are used for regulatory compliance verification, facility commissioning, operational optimization, and acceptance inspection of reclamation systems. Users should always confirm the latest published editions of the applicable standards, as revisions are issued periodically.
Testing Samples
The sample type and corresponding limit values depend entirely on the intended end use of the reclaimed water. The principal sample categories are described below.
Urban Miscellaneous Use Water
This category covers reclaimed water distributed through dedicated pipe networks for toilet flushing, urban greening and irrigation, road cleaning and dust suppression, vehicle washing, and construction activities such as dust control and concrete mixing. This is the most common reuse category for municipal and building-level systems, and it carries the strictest sanitary requirements because of potential public contact.
Scenic and Recreational Environment Water
This category includes water used to replenish ornamental lakes, landscape water bodies, artificial streams, and urban wetlands. The standard distinguishes between non-contact ornamental use and limited-contact recreational use, with stricter microbiological limits for the latter. Testing must also address eutrophication control parameters such as nitrogen and phosphorus to prevent algal blooms in stagnant water bodies.
Industrial Reuse Water
Industrial reclaimed water covers open recirculating cooling water, closed cooling systems, boiler feed makeup water, process and product contact water, and equipment washing water. In addition to sanitary indicators, testing must evaluate scaling and corrosion risk parameters such as hardness, chloride, sulfate, silica, and total dissolved solids to protect heat exchangers, boilers, and piping infrastructure.
Agricultural Irrigation Water
Reclaimed water used for farmland irrigation requires testing for parameters that affect crop safety and soil health, including salinity, sodium adsorption ratio, boron, heavy metals, and pathogen indicators. Different limit values apply to food crops, non-food crops, and different irrigation methods such as furrow, sprinkler, and drip irrigation.
Groundwater Recharge Water
This is the most demanding category, covering both surface spreading and direct well injection. Testing emphasizes comprehensive chemical and microbiological parameters, trace organic contaminants, and heavy metals to prevent aquifer contamination, along with long-term hydraulic and geochemical compatibility assessments.
Testing Items
Testing parameters are organized into functional groups based on the risks they control. Typical test panels are configured according to the applicable standard and the specific reuse scenario.
Physical and Sensory Indicators
- Chromaticity (color)
- Turbidity
- Odor
- Temperature
- Suspended solids (SS)
- Total dissolved solids (TDS)
Conventional Chemical and Nutrient Indicators
- pH value
- Biochemical oxygen demand (BOD5)
- Chemical oxygen demand (CODCr)
- Ammonia nitrogen (NH3-N)
- Total nitrogen (TN)
- Total phosphorus (TP)
- Anionic surfactants (MBAS)
- Petroleum and mineral oil
- Total hardness, alkalinity, chloride, and sulfate
- Iron, manganese, and silica
Microbiological and Sanitary Indicators
- Total coliform bacteria
- Fecal coliform and Escherichia coli
- Total heterotrophic plate count
- Legionella (particularly for cooling towers and aerosol-generating systems)
- Helminth eggs (for agricultural irrigation reuse)
Disinfection Residual Indicators
Residual chlorine concentration is a critical control parameter, as it must remain high enough to suppress microbial regrowth in distribution networks while avoiding excessive corrosivity or disinfection by-product formation. Both free chlorine and total chlorine are measured, and chlorine dioxide residual may be tested where alternative disinfectants are used.
Toxicological and Corrosion Control Indicators
- Heavy metals: lead, cadmium, chromium, arsenic, mercury, nickel, copper, zinc
- Cyanide and volatile phenols
- Langelier Saturation Index and Ryznar Index for scaling and corrosion tendency
- Chloride-to-sulfate mass ratio for corrosion aggressiveness assessment
Testing Methods
All analytical procedures follow national standard methods and industry technical specifications. Sampling is conducted in accordance with water quality sampling scheme standards, typically at the outlet of the reclamation facility, points along the distribution network, and the point of use.
Sampling and Preservation
Representative samples are collected in clean polyethylene or glass containers, with microbiological samples collected in sterile bottles containing sodium thiosulfate to neutralize residual disinfectant. Samples are preserved at low temperature and transported to the laboratory within defined holding times, and BOD5 analysis must begin promptly due to its short holding window.
Physical and Chemical Analysis Methods
- pH: glass electrode method (GB/T 6920)
- COD: dichromate reflux titration (HJ 828) or rapid digestion spectrophotometry (HJ/T 399)
- BOD5: dilution and seeding method with five-day incubation (HJ 505)
- Ammonia nitrogen: Nessler reagent or salicylate spectrophotometry (HJ 535, HJ 536)
- Total nitrogen: alkaline potassium persulfate digestion UV spectrophotometry (HJ 636)
- Total phosphorus: ammonium molybdate spectrophotometry (GB/T 11893)
- Turbidity: nephelometric method
- Suspended solids: gravimetric filtration (GB/T 11901)
- Total hardness: EDTA titration (GB/T 7477)
- Anionic surfactants: methylene blue spectrophotometry (GB/T 7494)
- Petroleum: infrared spectrophotometry (HJ 637)
- Chloride, sulfate, and other anions: ion chromatography (HJ 84)
Microbiological Analysis Methods
- Total coliform: membrane filtration (HJ 347.1) or multi-tube fermentation (HJ 347.2)
- Coliform bacteria and E. coli: enzyme substrate method (HJ 1001)
- Heterotrophic plate count: plate culture method
- Legionella: selective culture and confirmation
Instrumental and Online Monitoring Methods
- Heavy metals: inductively coupled plasma mass spectrometry (HJ 700) or inductively coupled plasma emission spectrometry (HJ 776)
- Residual chlorine: DPD spectrophotometry or electrochemical probes (HJ 586)
- Online continuous monitoring: real-time analyzers for pH, turbidity, residual chlorine, COD, and ammonia installed at reclamation plant outlets and key network nodes, supporting automated regulatory data reporting
Applications
Reclaimed water quality testing services support a wide range of engineering, regulatory, and operational scenarios:
- Acceptance testing and commissioning of municipal wastewater reclamation plants and distribution networks
- Ongoing operational compliance monitoring for treatment facilities and pumping stations
- Industrial water recycling programs in power generation, petrochemical, steel, paper, and electronics manufacturing, including cooling tower and boiler system protection
- Building-level greywater and rainwater harvesting systems in commercial complexes, hotels, hospitals, and residential communities
- Green building certification documentation for water reuse credits under LEED, China Three-Star, and comparable rating systems
- Landscape, golf course, and park irrigation management
- Agricultural reuse scheme verification and soil impact assessment
- Environmental impact assessments, ecological replenishment projects, and groundwater recharge programs
- Due diligence investigations for water-intensive industrial siting and water rights transactions
FAQ
How often should reclaimed water quality be tested?
Monitoring frequency depends on the reuse category and regulatory requirements. For urban miscellaneous water, operational indicators such as residual chlorine and turbidity are typically checked daily, chemical indicators such as COD and BOD5 weekly, and microbiological indicators monthly or quarterly, with comprehensive third-party verification at least once or twice per year. Industrial users often increase frequency based on equipment criticality.
Which standard applies to my project?
The applicable standard is determined by the end use: GB/T 18920 for urban miscellaneous use, GB/T 18921 for scenic environment use, GB/T 19923 for industrial use, GB 20922 for farmland irrigation, and GB/T 19772 for groundwater recharge. When a project serves multiple uses, the strictest applicable limit for each parameter governs.
How much sample is required and how should it be handled?
A routine physical and chemical panel typically requires 1 to 2 liters collected in clean polyethylene bottles, while microbiological testing requires sterile bottles of at least 150 milliliters. Samples should be kept cool, protected from light, and delivered to the laboratory as quickly as possible, as parameters such as pH, residual chlorine, and microbiological counts have very short holding times.
How long does testing take?
Standard physical and chemical parameters are usually reported within 5 to 7 working days. BOD5 inherently requires a five-day incubation period, and full comprehensive panels including microbiology and metals are typically completed within 7 to 10 working days.
What should be done if results exceed the limits?
Exceedances should trigger verification sampling to rule out sampling or analytical error, followed by diagnosis of the treatment process, such as disinfection dosing, membrane performance, or nutrient removal efficiency. Corrective actions must be documented, and the affected reuse point may need to be suspended until compliance is restored and confirmed by retesting.