ORP (Oxidation-Reduction Potential) 

Oxidation-reduction potential summarises whether water is oxidizing or reducing, in millivolts. It is used to control disinfection, to distinguish aerobic, anoxic and anaerobic zones in wastewater treatment, and to map redox conditions in groundwater remediation.

RAECO Rents supplies ORP instruments and combination pH/ORP sensors with NIST-traceable calibration included. Free ground shipping and free return shipping are included on every rental.

YSI ProDSS Multiparameter Digital Water Quality Meter
Frequently Asked Questions
Common questions about orp (oxidation-reduction potential)
What does ORP actually tell me?
Whether the water is oxidizing or reducing overall, in millivolts. Positive values mean oxidizing conditions, negative mean reducing. It is not a measure of any single substance — it summarizes the redox state produced by everything present, which makes it a diagnostic parameter rather than a compliance number.
Do I calibrate ORP the same way as pH?
No — ORP is a single point, typically against Zobell solution, and many instruments adjust the calibration value for temperature automatically. If you are using a combination pH/ORP sensor, calibrate pH first to confirm the sensor is responding properly before calibrating ORP.
Why is ORP used to control disinfection?
Disinfection effectiveness tracks redox potential more directly than residual concentration alone does. A residual figure tells you how much disinfectant is present; ORP tells you what the water is actually doing chemically. Most operators use both together rather than either on its own.
Should I rent a pH-only sensor or a combination pH/ORP sensor?
Take the combination sensor if there is any chance you will want ORP, since it delivers both parameters from a single port and leaves the remaining ports free for other measurements. Take pH-only when ports are tight and ORP is definitely not part of the scope.
How do I know when an ORP sensor is worn out?
Perform a factory reset on the sensor, then compare its millivolt reading in Zobell solution against the solution's calibration value. The difference should be under 100 mV. At 80 mV or more, the sensor is nearing the end of its life and should be replaced rather than nursed along.
My ORP readings drift or take a long time to settle. What now?
If it takes more than about 90 seconds to stabilize in Zobell, clean and recondition the sensor. Check the calibration solution has not expired, since ORP standards degrade. Typical working life for an ORP sensor is roughly 12 to 24 months depending on use, storage and maintenance.
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YSI ProDSS Multiparameter Digital Water Quality Meter
Water Quality Meter

YSI ProDSS Multiparameter Digital Water Quality Meter

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