What Tools Are Used in Water Quality Monitoring?

Water quality analysis involves evaluating the chemical, physical, and biological suitability of water for a specific application. Water parameter requirements for a fish farm will differ from those of a pharmaceutical manufacturing facility.

To achieve precise monitoring, a range of water quality measurement instruments is required. These instruments must have different ranges, resolutions, accuracies, response times, and repeatabilities to suit the specific application. Sensors are one of the essential tools required for monitoring water quality. You will also need test strips, water samplers, data loggers, and transducers to have a complete water monitoring setup.

To understand the significance of water quality monitoring, consider the regulations of the WHO and other global and regional organizations for drinking water. Poor water quality not only causes substandard products, material damage, and a reduction in the life of machinery, but in some cases, it also severely harms human health and the broader economy. This article aims to provide you with all the essential water quality monitoring parameters, water quality measurement tools, and their significance in various applications.

Regulatory Standards and Their Role in Monitoring

There are numerous organizations that regulate water quality requirements for specific usage scenarios. Some offer more strict control in comparison to others. For example, if we follow the EPA (U.S.) and EC (EU) requirements, we also meet the requirements of the WHO and ISO (global) guidelines. The EPA and EC are local bodies that offer far stricter water quality control compared to global organizations. For industrial use, standards can vary from one industry to another.

Some organizations may require monitoring dissolved oxygen (DO) levels in water, while others may only need to monitor pH and temperature. The regulatory standards ensure that the water is suitable for the particular application. Here are some examples:

▋Environmental Monitoring

• WHO & UNEP: global guidelines & ecosystem monitoring.
• ISO (5667 series): standard sampling methods.
• U.S. EPA (Clean Water Act) & EU Water Framework Directive: core regional regulators.
• National Agencies (e.g., USGS, China MEE, CPCB India, Pak-EPA, Japan MOE): implement and enforce locally.

▋Drinking Water Supply & Treatment

• WHO: Guidelines for Drinking-Water Quality.
• U.S. EPA (SDWA) & EU Drinking Water Directive: enforceable standards.
• National Ministries/Authorities (e.g., Health Canada, NHMRC Australia, SASO, PSQCA, BIS): Local adoption.

▋Wastewater & Industrial Effluents

• U.S. EPA (CWA, NPDES permits)
• EU Urban Waste Water Directive
• National Environmental Protection Agencies (China MEE, CPCB, Pakistan EPA, Japan MOE): Effluent Standards.

▋Aquaculture & Agriculture

• FAO: Aquaculture Guidelines.
• EU Nitrates Directive & U.S. EPA: Agricultural Water Standards.
• National Agriculture Ministries (e.g., ICAR India, MARA China): local enforcement.

According to the WHO, microbiologically contaminated drinking water can transmit diseases such as diarrhoea, cholera, dysentery, typhoid, and polio, which are estimated to cause approximately 505,000 diarrhoeal deaths each year. This is just one of the many ways water quality can impact our lives.

Instruments for Measuring Physical Parameters

Physical parameters of water refer to those that affect its appearance, taste, and usability. They are observable, tangible properties of water. Here are some key physical parameters observable using water quality sensors:

▪ Temperature

In broader terms, temperature is the measure of kinetic energy in water. It is a key indicator of water's set point for the change of phase. There are tremendous uses of monitoring water temperature in industry.

Monitoring temperature is vital in aquatic life, chemical reactions, and power plants. Their simple design makes them highly reliable for such applications. It typically uses material like platinum in RTDs or semiconductors in thermistors. The change in temperature of the sensor causes the material resistance to change. The change in resistance is electronically detected and converted into a temperature reading.

▪ Turbidity and Total Suspended Solids (TSS)

In the water purification process and environmental health monitoring, turbidity and TSS sensors detect the cloudiness of water. The degree of cloudiness represents the amount of suspended matter in water, including silt, algae, and microscopic organisms. The presence of these matters can reduce the quality of drinking water and clog fish gills, blocking the sunlight needed for aquatic plant photosynthesis.

These sensors utilize the Tyndall effect, which is the scattering of light by water containing suspended particles. The sensor passes light through the water and measures the amount of light that passes through to water. If the light passes is low, it means that it has high turbidity and TSS. Turbidity and TSS are measured in Nephelometric Turbidity Units (NTU) and TSS (often in mg/L), respectively.

▪ Electrical Conductivity (EC), Salinity, and Total Dissolved Solids (TDS)

The presence of salts in water increases its conductivity. Therefore, a single sensor that measures the water's conductivity is capable of detecting EC, salinity, and TDS. Salinity is the presence of salts in water, and TDS is also a measure of dissolved salts (ions) in water. As all these parameters are closely related, a single sensor is enough to provide results.

A sensor that measures EC, TDS, and Salinity uses two electrodes dipped into the water. They pass current through the water and measure the water resistance. Lower resistance means higher conductivity, salinity, and TDS. However, they are sensitive to temperature and require calibration of the correlation factor based on the type of solution.

▪ Water Level

Although not directly related to the quality of water, but water level is a crucial parameter to monitor reservoirs and river flow. It is often used in water quality monitoring. Here are some types of water level sensors:

• Submersible Hydrostatic Level Sensors
• Ultrasonic Water Level Sensors
• Radar Water Level Sensors
• Capacitive Level Sensors
• Float-type Level Sensors

Instruments for Measuring Chemical Parameters

Beyond the visible appearance, taste, and usability is the presence of chemicals in water. They are not directly observable by the human eye. You may need specialized sensors that can detect the presence of chemicals in water. Some detectors combine all these sensor parameters into a single unit. There are some of the most advanced sensors, like the RK500-09. However, to make it easy to understand, here we will mention them separately:

♦ pH and ORP

pH (Potential for Hydrogen) is a key indicator of water's ability to react with chemicals and indicate its ability to cause corrosion. ORP (Oxidation-Reduction Potential) is the water's ability to act as an oxidizing or reducing agent. Measuring pH and ORP is key in water quality monitoring, as it collectively provides information on a water's acidity or alkalinity, as well as its sanitizing power and overall health.

A pH sensor utilizes a glass tube that is permeable to hydrogen ions as an electrode, while ORP sensors employ a noble metal measuring electrode, such as platinum or gold. Both require a reference electrode that is provided with a stable voltage. The difference in voltage between electrodes gives pH and ORP, respectively. They are often integrated into a single sensor as they use similar hardware and a reference electrode.

♦ Dissolved Oxygen (DO)

DO is critical for aquatic life as it is a direct indicator of the presence of oxygen in water. However, in the case of the process industry, DO is often unwanted, as it can enhance the corrosion process when it comes into contact with metals. Therefore, the ranges and minimum readings may differ in both applications.

There are two types of DO sensors utilizing electrochemical or optical technologies. Electrochemical type uses a membrane to allow oxygen diffusion, which then causes a chemical reaction with electrodes to generate an electrical signal proportional to the DO level. Optical sensors, also known as luminescence-based sensors, utilize a fluorescent dye that is "quenched" (i.e., its light emission is reduced) by oxygen.

♦ Nutrients (Ammonium, Nitrates, and Nitrites)

Monitoring nutrients such as ammonium, nitrates, and nitrites is crucial in fields like water treatment, environmental monitoring, agriculture, and aquaculture. Effluent discharge from wastewater treatment, eutrophication in rivers and lakes, and measurement of nutrients in soil are all key areas to monitor the presence of nutrients.

Ion-Selective Electrodes (ISEs), Optical Sensors, and Colorimetric Analyzers are the working mechanisms in these sensors. Each nutrient will have its specific sensor.

♦ Chemical and Biological Oxygen Demand (COD/BOD)

Some pollutants in water require oxygen to break down. Therefore, it's necessary for us to determine the amount of oxygen these pollutants require to eliminate them from the water and stabilize the oxygen levels. COD/BOD is the amount of oxygen needed to break down the pollutants in water. It is a key indicator used to assess the degree of water pollution and the efficiency of wastewater treatment processes.

Organic and inorganic matter in water absorbs UV light of different wavelengths. Passing UV light through a water sample and analyzing the output at different wavelengths provides an overall picture of the presence of organic and inorganic matter in water.

♦ Residual Chlorine

In water quality monitoring, chlorine is added to the water to kill pathogenic microorganisms that can be a health hazard. Chlorine may be monitored at two stages. Initially, the aim is to kill microorganisms that are dangerous for consumption, and later, when it is supplied for drinking purposes. According to regulatory requirements, maintaining a safe chlorine level is crucial for ensuring the quality of drinking water.

A sensor's working electrode reacts with chlorine ions in the water to produce an electrical current. The current signal is then sent to a controller that converts the signal into tangible values for HMI devices.

Instruments for Measuring Biological Parameters

The presence of certain living organisms in water can be dangerous for human consumption. Monitoring these parameters in the production of drinking water is key. Let's analyze these parameters and how we can detect them:

● Cyanobacteria (Blue-Green Algae)

Blue-Green Algae, also known as Cyanobacteria, appears in the form of dense, visible blooms in warm, nutrient-rich water. They pose a serious health problem as they produce toxins that can cause liver damage, neurological problems, skin irritation, and even death.

Detecting cyanobacteria requires Optical Fluorescence sensors. Sensors emit light (excitation) at a specific wavelength (usually around 590–630 nm). In return, the Phycocyanin in cyanobacteria absorbs this light and then emits fluorescence at a longer wavelength (~650–660 nm). Detecting the light represents the presence of Cyanobacteria in water.

● Chlorophyll

Chlorophyll is a key indicator of phytoplankton biomass presence in water. It gives an overall picture of the water quality and ecosystem health. The presence of algal blooms can cause issues like poor taste and odor in drinking water, depletion of oxygen, and the creation of toxic conditions.

It also utilizes optical fluorescence sensors, similar to those used in cyanobacteria detection mentioned earlier. The sensor usually emits a blue LED (~470 nm) into the water, which Chlorophyll-a in algae absorbs and re-emits as red light (~680 nm). The intensity of the red light detected indicates the presence of chlorophyll.

Advanced Water Quality Monitoring System

The sensor alone is insufficient to initiate water quality monitoring. To initiate the monitoring process, you will need the following components. There are advancements in each part of the water quality monitoring system. We will mention the latest and the best:

• Data Logger/Controller: Collects data from sensors and stores it using RS-485 Modbus, SDI-12, and 4–20 mA signals.
• Power Supply: AC mains, DC batteries, or solar panels
• Telemetry/Communication System: It transmits data to the monitoring center using GSM/4G modems, LoRa, Wi-Fi, and satellite uplinks.
• Mounting & Housing Hardware: Submersible probes need suspension cables or wells. Whereas, Non-contact sensors (radar/ultrasonic level) need stable mounts. Some will come with protective casings (anti-corrosion, anti-fouling, anti-theft).
• Calibration Solutions & Accessories: You may need standard solutions (e.g., pH 4.0, 7.0, 10.0 buffers; DO zero-oxygen solution; turbidity standards) and cleaning kits or auto-clean wipers to ensure repeatability and reliability in results.
• Software & Dashboard: SCADA, cloud dashboards, or PC/mobile apps to visualize data trends.

The ability of these water quality monitoring tools to transmit data wirelessly to a central monitoring station enables the collection and analysis of live data. The authorities can take quick actions and ensure compliance with regulatory requirements.

Recommended Sensors for Water Quality Monitoring

Conclusion

Maintaining water quality requires a comprehensive system of equipment that works in tandem to produce accurate results. To ensure reliable results, you need sensors, data loggers, transmission, mounting, power supply, and calibration processes. The most important thing is the sensor. Each sensor can be unique with its working mechanism and application. Meeting water quality standards, as regulated by global and regional organizations, requires a careful evaluation of the physical, chemical, and biological parameters of water. It allows timely action to control or eliminate the presence of harmful substances.

If you are looking for a one-stop solution for all your water quality monitoring needs, visit the RIKA website and contact the representative. Rika Sensor provides the most extensive after-sales and end-to-end project deployment services. The water quality measurement instruments are of the highest quality and produce the most accurate results, backed by long warranties. Visit the RIKA website to learn more.

Frequently Asked Questions

1) Can water quality monitoring prevent waterborne diseases?

Yes, monitoring water quality continuously using sensors that detect physical, chemical, and biological parameters can help prevent waterborne diseases. Detecting harmful microorganisms and chemical contaminants enables a proactive approach to treating the water or shutting down compromised systems before the water reaches human consumption.

2) What is a water quality index?

To simplify the quality of water, the water quality index (WQI) converts complex data into a single numerical score. It helps the public and policymakers understand water quality immediately. It represents parameters like pH, DO, and turbidity.

3) What is the difference between biological and chemical water quality parameters?

Biological elements in water are living organisms that can have a harmful effect on the human body or aquatic life. Therefore, detecting it is also a key part of water quality. Moreover, the presence of chemicals like nutrients, chlorine, DO, pH, and ORP is also vital to ensure that the water remains suitable for human consumption.