ORP (Oxidation-Reduction Potential)
ORP is the electrical potential of water measured in millivolts that indicates the overall oxidising capacity of the water.
Definition
ORP is the electrical potential of water measured in millivolts that indicates the overall oxidising capacity of the water.
Typical Values: Sanitation threshold: 650 mV; Optimal: 700–750 mV
In Plain Language
ORP is measured with a probe and reflects the combined effect of free chlorine concentration and pH on the water's ability to oxidise contaminants. At an ORP above 650 mV, water is generally considered effective for sanitation. ORP is not a direct chlorine measurement — the same free chlorine reading produces very different ORP values at different pH levels. It is a useful supplemental indicator but does not replace direct chemical testing.
Why It Matters
ORP probes provide a real-time, continuous indication of sanitiser activity without requiring reagent-based tests.
Typical Values
Sanitation threshold: 650 mV; Optimal: 700–750 mV
Last reviewed: 2026-06-01