--- title: "Resistivity Sensors & Monitoring | Aethair" description: "Resistivity measures how strongly water resists an electric current (the inverse of conductivity) and is reported by the three sonde families shown here." url: https://aethair.io/parameters/resistivity/ --- Measurements · Water Quality # Resistivity Also known as specific resistance Resistivity is how strongly water resists an electric current (the inverse of conductivity), so the purer the water, the higher its resistivity. [Schedule a call](https://calendly.com/d/ctdd-mkr-v9v/aethair-demo-website) [Configure Resistivity Monitoring](https://aethair.io/build/?params=resistivity) At a glance MΩ·cm Water Quality 1 way to measure it - **Thiamis** 3 external instruments What it is ## What is resistivity? Resistivity is how strongly water resists an electric current (the inverse of conductivity), so the purer the water, the higher its resistivity. On this platform it is part of the conductivity set a multiparameter water-quality instrument reports, alongside conductivity, specific conductance, salinity, and TDS. Three instrument families in the sensor catalog report it: - the [In-Situ Aqua TROLL](https://aethair.io/sensors/in-situ-water-quality-sondes/) CTD loggers and multiparameter sondes (the Aqua TROLL 100, 200, 400, 500, and 600), in Ω·cm; - the [YSI 6-Series](https://aethair.io/sensors/ysi-water-quality-sondes/) multiparameter sondes (the 6600, 6920, 6820, and 600-series), in MΩ·cm, kΩ·cm, or Ω·cm; - the [Spectra Scientific Spectra Litmus](https://aethair.io/sensors/spectra-scientific-water-quality-sondes/) configurable sondes (Litmus 6 and Litmus 4), in MΩ·cm. How it is measured ## How Resistivity Is Measured Each is a sonde reporting its conductivity cell's readings, read by a [Thiamis](https://aethair.io/products/thiamis/) gateway. The In-Situ and Spectra Litmus instruments are polled over Modbus RS-485. The YSI 6-Series is read over SDI-12. Its response is an ordered list of values with no labels, so the sensor order configured in YSI's software when the sonde is prepared determines which value is resistivity. A deployment reports only the parameters it was set up for. The YSI 6-Series sondes and the Spectra Litmus are discontinued by their makers, so on the platform they mostly serve existing deployments. An instrument on Thiamis 3 A third-party instrument connected to a Thiamis gateway, reporting into the same Environet account. ### Every device and option that measures Resistivity 3 | Device / option | Type | Base platform | Measures | | - | - | - | - | | [In-Situ](https://aethair.io/sensors/in-situ-water-quality-sondes/) · Level TROLL 300, Level TROLL 400, Level TROLL 500… | Water Quality Sondes | Thiamis | Resistivity [Dissolved Ammonia (NH₃)](https://aethair.io/parameters/ammonia/) [Ammonium (NH₄)](https://aethair.io/parameters/ammonium/) [Blue-Green Algae](https://aethair.io/parameters/bga/) [Chloride](https://aethair.io/parameters/chloride/) [Chlorophyll](https://aethair.io/parameters/chlorophyll/) [Conductivity](https://aethair.io/parameters/conductivity/) | | [Spectra Scientific](https://aethair.io/sensors/spectra-scientific-water-quality-sondes/) · Spectra Litmus 6, Spectra Litmus 4 | Water Quality Sondes | Thiamis | Resistivity [Dissolved Ammonia (NH₃)](https://aethair.io/parameters/ammonia/) [Ammonium (NH₄)](https://aethair.io/parameters/ammonium/) [Blue-Green Algae](https://aethair.io/parameters/bga/) [Chloride](https://aethair.io/parameters/chloride/) [Chlorophyll](https://aethair.io/parameters/chlorophyll/) [Conductivity](https://aethair.io/parameters/conductivity/) | | [YSI](https://aethair.io/sensors/ysi-water-quality-sondes/) · 6600 V2, 6600EDS V2, 6920 V2… | Water Quality Sondes | Thiamis | Resistivity [Dissolved Ammonia (NH₃)](https://aethair.io/parameters/ammonia/) [Ammonium (NH₄)](https://aethair.io/parameters/ammonium/) [Blue-Green Algae](https://aethair.io/parameters/bga/) [Chloride](https://aethair.io/parameters/chloride/) [Chlorophyll](https://aethair.io/parameters/chlorophyll/) [Conductivity](https://aethair.io/parameters/conductivity/) | [Configure Resistivity Monitoring](https://aethair.io/build/?params=resistivity) Related ## More in Water Quality [Water Temperature](https://aethair.io/parameters/water_temperature/) [pH](https://aethair.io/parameters/ph/) [ORP](https://aethair.io/parameters/orp/) [Specific Conductance](https://aethair.io/parameters/specific_conductance/) [Salinity](https://aethair.io/parameters/salinity/) [TDS](https://aethair.io/parameters/tds/) [Turbidity](https://aethair.io/parameters/turbidity/) [Dissolved Oxygen](https://aethair.io/parameters/do/) [Chlorophyll](https://aethair.io/parameters/chlorophyll/) [Nitrate (NO₃)](https://aethair.io/parameters/nitrate/) [Ammonium (NH₄)](https://aethair.io/parameters/ammonium/) [Dissolved Ammonia (NH₃)](https://aethair.io/parameters/ammonia/) Questions ## Resistivity FAQ Which instruments report resistivity? The In-Situ Aqua TROLL 100, 200, 400, 500, and 600, the YSI 6-Series sondes, and the Spectra Scientific Spectra Litmus 6 and Litmus 4. How does a YSI 6-Series sonde report resistivity over SDI-12? As one value in an ordered, unlabeled list. Its meaning is set by the sensor order configured on the sonde, and a deployment reports only the parameters it was prepared for. In what units is resistivity reported? Ω·cm on the In-Situ instruments, MΩ·cm on the Spectra Litmus, and MΩ·cm, kΩ·cm, or Ω·cm on the YSI 6-Series.