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Horiba W-21SDI Water Quality Monitoring System

Horiba U-21SDI Multiparameter Water Quality Meter
Horiba U-21SDI Multiparameter Water Quality Meter
Model NumberPart Number
W-21SDI set; 2/10M cable case 201031-5
W-21SDI set; 30+M cable case 201031-5
Packing List: No cable. Sensor probe, control unit, DO and pH/ORP sensors, 100-4 pH 4 buffer, carrying case, DO rebuild kit, 330 internal soln., calibration beaker, batteries, instruction manual, consumables.


  • Simultaneous monitoring of up to 8 water quality parameters.
  • Dry cell battery operated meter.
  • Up to one month data logging.
  • Measurement at depths as low as 100 meters.


When it comes to being vigilant about water quality, the Horiba W-21SDI is an essential tool for field use. The multipurpose W-21SDI allows for simultaneous monitoring of up to eight different parameters:

  • pH
  • Dissolved oxygen (DO)
  • ORP • Salinity
  • Conductivity
  • Total dissolved solids (TDS)
  • Seawater specific gravity
  • Temperature

Featuring a high pressure tolerance that allows it to be deployed at depths up to 100 meters, the W-21SDI can be used for both long-term monitoring and periodic water quality checks. Contact Environmental Equipment & Supply for information about pricing and available accessories.

SDI-12 Compatible

The HORIBA W-21SDI can now interface with SDI-12 compatible data collection platforms and integrate into third party monitoring systems. SDI-12 is a communications protocol commonly used with environmental monitoring equipment that allows for collecting log data from multiple devices over a single line. SDI-12 connectivity is prized by environmental professionals for its low power requirements, making it ideal for linking devices in the field.


Horiba water quality monitoring systems are used for a number of different environmental applications where collecting readings of several parameters at once is required. Typical uses of the W-21SDI include monitoring TMDL (total maximum daily load), storm water runoff, non-point source pollution, combined sewer overflows and wastewater effluent, as well as general studies conducted in rivers, lakes, estuaries and aquifers.

Data Logging Options

True to its purpose as a multifunctional research tool, the Horiba W21SDI includes memory for up to a month of data readings collected at 15 minute intervals. This makes it ideal for continual deployment, as it can be installed in an aquifer for an extended period of time without having to worry about maintenance. Data can even be collected remotely using an SDI-12 compatible device.

Probe Details

A powerful Horiba probe is key to the W-21SDI’s expanded functionality as a water quality monitoring system. Measuring 46mm OD, it can easily be deployed in smaller wells and boreholes at temperatures between 0°C and 55°C. The probe comes standard with conductivity, salinity, TDS, seawater specific gravity and temperature sensors. Optional are additional sensors for pH, DO and ORP. All sensors employ the sophisticated electrode technology Horiba has become known for in over 60 years as a leading manufacturer of water quality monitoring instruments.

Buy the W-21SDI Multiparameter Water Quality Meter Now!

Parts & Accessories
Probe and Cables
Sensors Not Included
Part Number
W-21SDI sensor probe 351558
2 meter cable, W002CS G0047241
10 meter cable, W010CS G0047251
30 meter cable, W030CS G0047261
60 meter cable, W060CS G0157320
100 meter cable, W100C G8087902
Data Logging Optional AccessoriesPart Number
U-2001 extension unit, software 370098
RS-232C cable 530200
AC adapter 362063
U-2002 GPS, extension unit, carrying case, battery pack, printer and cables 370097

Replacement Sensors &
Maintenance Parts
Part Number
Dissolved oxygen sensor 9037005800
pH/ORP sensor 9037005700
DO rebuild kit 9037007400
DO membranes; 10 rebuilds G0191720
DO sensor 305 solution G8088130
pH sensor 330 solution 362178
DO/pH sensor O-rings, 2/set 9037007600
Calibration SolutionsPart Number
100-4 pH 4 buffer 350623
100-7 pH 7 buffer 350624
100-9 pH 9 buffer 362172
71.8 mS/m conductivity 0.5L 201045-5
71.8 mS/m conductivity 1L 201046-5
0.667 S/m conductivity 0.5L 201045-6
0.667 S/m conductivity 1L 201046-6
5.87 S/m conductivity 0.5L 201045-7
5.87 S/m conductivity 1L 201046-7
DO zero powder; 0.5L btl. 201045-2
DO zero powder; 1L btl. 201046-2
89mV ORP check 201045-1
258mV ORP check 201046-1

Miscellaneous PartsPart Number
W-2000S control unit 530675
Grip holder, blue 9037007700
Flow cell 370373
Calibration beaker 9037008600
Sensor guard cover, plastic 9037007300
Carrying case, 2/10 meter 362484
Carrying case, 30+ meters 362485
SST W-2200 sensor cage 362483
Silicone grease F1000138900
Control unit connector cover 9037007100
Spanner wrench 9037007200
Syringe, 10ml F0020856600
Control unit PC board H2022777001
Control unit battery packing 9096001300
Extension unit O-ring 9096001400
Sensor port plugs 9037007100