Could it be chlorophinols that you are mistaking for astringency? Not all RO systems are capable of reducing chloramine levels very well. The key is lots of contact time with carbon. This is why some systems have two carbon blocks before the membrane and one after. More before the membrane couldn't hurt. Some makers sell carbon blocks specific to chloramine, but I have seen some say it isn't worth the extra expense.
I'm not an expert, just what I have gathered while researching home RO systems.