When is it necessary to replace RO membranes?

The correct answer is that RO membranes should be replaced if the RO rejection rate reaches 80%. This is important because the RO rejection rate indicates how effectively the membrane is filtering out unwanted solutes from the water. A rejection rate of 80% means that the membrane is allowing a significant amount of impurities to pass through, which compromises the quality of the treated water.

Maintaining a high rejection rate is crucial for ensuring that the water meets safety and quality standards, especially in applications where water purity is critical. If the rejection rate dips below the desired level, it is an indication that the membrane may be fouling, scaling, or degrading, thus necessitating its replacement to maintain system performance.

Other options do not align with the established guidelines for membrane replacement. Annual replacement may not be warranted for all systems, as the lifespan can greatly vary depending on usage and water quality. A TDS meter failure does not directly indicate membrane condition, and significant water pressure drops can be caused by various factors that do not necessarily signal a need for membrane replacement. Thus, monitoring the RO rejection rate is a more reliable approach to determine when to replace RO membranes.