in relation to a desalination water plant why is dew point regarded as important .
It's an reverse osmosis plant,it was an interview question even though i didn't get the job that was one of the ice breaker question.Hmmm, The answer to that would require more context. And there are many types of desalination plants (evaporative; reverse osmosis; etc.).
Have you tried looking at the plant Operations Manuals?
Have you tried using your preferred World Wide Web search engine to search for information on the type of desalination plant you are working at, or are considering trying to work at, or are studying in school?