Water Quality Sensors

What water quality sensors measure

A water quality sensor converts a physical or chemical property of water into a signal that a data logger, controller or telemetry system can read. The Zata IoT range covers twelve measurement categories: multi-element (combined) probes, conductivity, pH, turbidity, COD, ammonia nitrogen, transparency, ORP (oxidation-reduction potential), fluoride, chloride, chlorophyll and residual chlorine. Each sensor targets one or more of these parameters and reports the reading over an RS485 Modbus RTU interface, which is the standard protocol used across the range so that different sensor types can share a single data logger or SCADA input.

How the measurement technology works

Zata sensors use four main measuring principles, and which one applies depends on the parameter.

Electrode-based sensors, used for pH, conductivity, ORP, ammonia nitrogen, fluoride and chloride, place a sensing element in direct contact with the water. pH and ORP sensors use a glass electrode. Conductivity uses a quadrupole graphite electrode. Ammonia, fluoride and chloride sensors use ion-selective electrodes that respond to a specific ion concentration. Most electrode sensors in the range are housed in POM (polyoxymethylene) plastic bodies with a 3-metre cable and an NPT 3/4 thread for installation.

Optical sensors, used for turbidity, chlorophyll, blue-green algae (cyanobacteria) and water transparency, shine light into the water and measure how much is scattered, absorbed or fluoresced back. Turbidity sensors (model ZWQ-TUB1) use infrared LED scattering through a sapphire optical fibre. Chlorophyll and blue-green algae sensors use fluorescence, exciting pigments in algae and measuring the light they emit. COD and transparency sensors use ultraviolet or near-infrared absorption spectrometry, where the amount of light absorbed as it passes through the water sample correlates with organic content or clarity.

Fluorescence-based dissolved oxygen sensors measure the quenching of a fluorescent coating by oxygen molecules, which removes the need for the electrolyte and membrane replacement required by older Clark-cell designs.

The residual chlorine sensor (ZWQ-CT1) is the exception in the range: it uses a Clark-type amperometric electrode which requires a continuous flow of sample water (250-500 mL/min) and constrains the pH (4-9) and conductivity (10-50,000 µS/cm) of the sample for accurate readings.

Key specs to compare before buying

Four figures matter most when comparing sensors within a category.

Measurement range tells you whether the sensor covers your expected concentration. For example, the conductivity sensor (ZWQ-CND1) covers 0-200,000 μS/cm, while the residual chlorine sensor (ZWQ-CT1) only covers 0-2 mg/L, reflecting the very different concentration scales these two parameters occupy in real water samples.

Accuracy and resolution determine how precise the reading is. Accuracy is usually expressed as a percentage of reading (for example ±1% for conductivity) or as an absolute figure (±0.1 pH for the pH sensor). Resolution is the smallest change the sensor can detect, such as 0.01 μS/cm for conductivity or 0.001 mg/L for residual chlorine.

Response time matters for process control applications where readings need to update quickly. Most electrode sensors in the range respond in under 15 seconds; the dissolved oxygen sensor takes under 45 seconds because fluorescence quenching is inherently slower than a direct electrode reaction.

Materials and self-cleaning affect maintenance. Sensors exposed to fouling risk, such as turbidity, COD, chlorophyll, blue-green algae and transparency sensors, include a self-cleaning wiper or brush and use 316L stainless steel or titanium alloy housings for durability in continuous deployment. Electrode-only sensors (pH, conductivity, ammonia, fluoride, chloride, ORP) use POM housings, which are lighter and adequate for probes that are not mechanically wiped.

Typical applications and industries

Surface water and groundwater monitoring account for most of the applications listed across the range, covering rivers, lakes, reservoirs and boreholes. The multi-parameter meter (ZWQ500) and individual probes are also specified for long-term unattended online stations, on-site rapid testing during fieldwork, and emergency response monitoring after a pollution incident. The residual chlorine sensor is the exception, targeting tap water, secondary water supply systems and swimming pools rather than open water bodies.

How to choose between models in this category

Start from the parameter you need to measure, not the sensor type. If you need several parameters at one site, the ZWQ500 multi-parameter meter combines temperature, pH, conductivity, dissolved oxygen and turbidity in a single probe body, with COD, chlorophyll or cyanobacteria available as factory options, which reduces the number of individual sensor points and cables at an installation.

If you only need one parameter, or need a wider range or better accuracy than the multi-parameter unit provides for that specific parameter, a dedicated single-parameter sensor is usually the better fit. For example, the standalone turbidity sensor (ZWQ-TUB1) is rated to 1000 NTU against the ZWQ500's shared turbidity channel rated to 4000 NTU, so the right choice depends on which unit's full specification matches your site's expected range.

Check the operating environment figures too. Most probes are rated DC 12V or 24V power and connect via RS485 Modbus RTU, but confirm cable length (3 metres is standard across the range), thread size (NPT 3/4 on most models) and whether your logger or PLC already supports Modbus RTU polling.

Buying through MetSensor UK

MetSensor UK is the UK reseller for the Zata IoT sensor range described on this page; we do not manufacture these sensors. Pricing is quote-based because installation thread, cable length, power supply and communication protocol options vary by project, so contact us with your parameter list and site requirements and we will confirm current lead times and configuration options. Support, technical queries and after-sales contact are handled from the UK.