A Monitor's Guide to Water Quality

Oxidation-Reduction Potential (ORP)

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In healthy lakes and rivers, ORP should be relatively high between 300-500 mV. In contrast, certain wetlands can contain water with naturally low ORP.

How is it measured?

ORP is measured directly in the water using an ORP sensor. ORP is measured in millivolts (mV) and can either be above zero or below zero.

ORP is influenced by: dissolved oxygen and other elements that may function chemically like oxygen (e.g., nitrate, sulfur, iron)

ORP influences : the form and toxicity of certain metals