Pourbaix diagrams are widely used to describe the behaviour of chemical species in the hydrosphere. In this context, reduction potential  is often used instead of . The main advantage is to directly work with a logarithm scale.  
 is a dimensionless number and can easily be related to  by the equation:
Where,  is the thermal voltage, with , the gas constant (), , the absolute temperature in Kelvin (298.15 K = 25 °C = 77 °F), and , the Faraday constant (96 485 coulomb/mol of ). Lambda, λ = ln(10) ≈ 2.3026. 
Moreover, 
: , an expression with a similar form to that of pH. 
 values in environmental chemistry ranges from −12 to +25, since at low or high potentials water will be respectively reduced or oxidized. In environmental applications, the concentration of dissolved species is usually set to a value between 10 M and 10 M for the determination of the equilibrium lines.