Conductivity / Temperature / Depth Sensor


Water level sensors—Why spend more for less?

The problem with most water depth, temperature, and electrical conductivity (EC) sensors is that their cost is prohibitively high. Plus they often require an extra barometric pressure sensor to correct for atmospheric pressure. You need a low-cost water level sensor equipped with everything necessary for things like tracking changes in solute movement, groundwater recharge, and surface water hydrology. You need HYDROS 21.

No need for costly extra sensors

A compact 3.4 cm diameter water level sensor that fits into tight spaces, the HYDROS 21 is a low-cost, durable, and easy-to-use tool for monitoring EC, temperature, and depth in both groundwater and surface water. More importantly, it’s an all-in-one instrument. When used with the ZL6 data logger or any other logging system, you won’t require an additional sensor for measuring—and referencing—barometric pressure. With a range of 0 to 120 dS/m and a measuring depth of 10 m, the sensor makes accurate depth and EC measurements for a broad range of applications.

Easy, research-grade data in real time

One of the qualities that makes the HYDROS 21 water level sensor so easy to use is its fast plug-and-play compatibility with the ZL6 data logger (also compatible with Campbell Scientific data loggers). Plus, with the ZL6, you can monitor and remotely access cloud data wirelessly from any internet-connected computer or device in near-real time.

Best price-to-performance ratio on the market

Trying to measure water level, temperature, and EC typically requires an expensive sensor with integrated telemetry. Unlike competitor sensors, all of the HYDROS 21’s data management happens in an external data logger, so the cost of each individual sensor is lower. Now, instead of having to rely on a single point measurement, you can take readings in several different locations without exceeding your budget.

Affordable, accurate, and reliable

While engineering the HYDROS 21 water level sensor, we wanted to design a water level sensor that was not only highly accurate but also provided a high degree of value. Because of its low-complexity, low-maintenance, and low-cost design, you can be assured you’re getting an instrument that will save you time, hassle, and money.

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  • Continuously monitor groundwater and surface water level changes
  • Vented sensor means no need for an additional sensor to measure and reference barometric pressure
  • Integrated electrical conductivity and temperature measurement
  • 3.4 cm diameter sensor that fits into tight spaces
  • Low cost
  • Durable
  • Easy to use


View GSA details


Bulk electrical conductivity (EC)

Range: 0−120 dS/m
Resolution: 0.001 dS/m
Accuracy: ±0.01 dS/m or ±10%, whichever is greater

NOTE: The EC measurement is corrected to a standard temperature of 25 °C.


Range: −11 to +49 °C
Resolution: 0.1 °C
Resolution: ±1 °C

Water depth

Range: 0−10,000 mm
Resolution: 1 mm
Accuracy: ±0.5% of full scale at 20 °C

NOTE: Depth measurement accuracy assumes no abrupt temperature variations.



DDI serial or SDI-12 communication protocol

Data logger compatibility

METER ZL6 data loggers and any data acquisition system capable of 3.6- to 15.0-VDC power and serial or SDI-12 communication



Length: 9.0 cm (3.5 in)
Width: 3.4 cm (1.3 in)

Operating temperature range

Minimum: 0 °C
Maximum: 50 °C

NOTE: Sensors may be used at higher temperatures under certain conditions; contact Customer Support for assistance.

Cable length

10 m (standard)
20 m
40 m (maximum cable length)

Cable diameter

6 mm

Connector types

3.5-mm stereo plug connector or stripped and tinned wires


Supply voltage (VCC to GND)

Minimum: 3.6 V
Maximum: 15.0 V

Digital input voltage (logic high)

Minimum: 2.8 V
Typical: 3.6 V
Maximum: 5.0 V

Digital input voltage (logic low)

Minimum: –0.3 V
Typical: 0.0 V
Maximum: 0.8 V

Digital output voltage (logic low)

Typical: 3.6 V

Power line slew rate

Minimum: 1.0 V/ms

Current drain (during measurement)

Minimum: 0.5 mA
Typical: 0.5 mA
Maximum: 1.0 mA

Current drain (while asleep)

Typical: 0.3 mA

Power up time (DDI serial)

Typical: 475 ms
Maximum: 500 ms

Power up time (SDI-12)

Minimum: 300 ms
Typical: 475 ms
Maximum: 500 ms

Measurement duration

Typical: 350 ms
Maximum: 500 ms


Manufactured under ISO 9001:2015
EM ISO/IEC 17050:2010 (CE Mark)

California requires the following notice:

⚠️ WARNING: This product may contain chemicals including ethylene glycol, lead, nickel, styrene and cadmium, which are known to the State of California to cause cancer, birth defects or other reproductive harm. For more information, go to www.P65Warnings.ca.gov



Have a question or problem? Our support team can help.

We manufacture, test, calibrate, and repair every instrument in-house. Our scientists and technicians use the instruments every day in our product testing lab. No matter what your question is, we have someone who can help you answer it.

Phone US: +1 509-332-5600
Phone Europe: +49 89 12 66 52 0


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