What is the difference between EPA and ISO when measuring turbidity?

EPA and ISO refer to the standard compliance methods for measuring turbidity.

EPA Method Turbidity

In turbidity instrumentation that runs in compliance with the EPA method, you are working with a methodology developed for testing drinking water in the USA. The turbidity meter will use a tungsten lamp for its light source. EPA-compliant turbidity meters perform better than ISO-compliant meters when you are measuring very low levels of turbidity. For a meter to be EPA-compliant, it must have an accuracy of < 0.05 NTU. Interferences from high turbidities or highly colored samples can occur.

ISO Method Turbidity

ISO compliant turbidity meters are more common than EPA method meters outside of the USA. This type of turbidity meter uses an infrared LED as its light source. ISO-compliant turbidity meters perform better in samples with high levels of turbidity, and in highly colored samples.