What is the BEST indication that the membrane module is damaged and is no longer semi-permeable and allowing the solute to pass through?

Correct Answer: Option D — High freshwater outlet salinity.

High freshwater outlet salinity indicates a breach in the semi-permeable membrane, allowing dissolved solids to bypass the filtration process. This failure compromises the unit's ability to reject solutes. In accordance with standard water quality monitoring, this condition requires immediate inspection and replacement of the compromised membrane module to ensure potability.