In what scenario would you most likely replace the RO membranes?

The scenario in which you would most likely replace the RO membranes is when the rejection rate is below 80%. RO (reverse osmosis) membranes are designed to filter out contaminants and impurities from water by rejecting particles based on size and charge. A rejection rate of 80% or higher indicates that the membranes are still functioning effectively, meaning they are adequately removing contaminants from the water.

When the rejection rate drops below 80%, it suggests that the membranes may be fouled, damaged, or otherwise compromised. Such a decrease in performance can lead to poor water quality and may not meet regulatory standards or health requirements for water supply. Therefore, replacing the membranes in this case is critical to restore their performance and ensure that the system is working properly.

The options relating to water temperature and pH are more about operational conditions that can affect membrane performance but do not directly trigger a membrane replacement decision. Operating at inappropriate temperatures or unstable pH levels can contribute to membrane degradation, but they do not serve as definitive thresholds for replacement like the rejection rate does.