RO systems will work great if they are properly maintained. After all, it was purchased so, you have clean drinking water however, if the filters are never changed, the water passing through them will soon go south. It is important to change the filters regularly, for an RO system to perform properly.
As the filters age, they become full of the contaminants they are supposed to remove. The longer they are left unchanged, they start to pass excess contaminants to the membrane which, can become overwhelmed and clogged. Since, the membrane is the most expensive filter of the system, you want it to last as long as possible.
The filters before the membrane should be changed often and the timing of changing these filters should be gauged on how much water is passing though them. The pre-filters before the membrane should be changed at 1500 gallon intervals maximum. When 1500 gallons of water has been filtered by the pre-filters, these filters will gradually start to pass on the contaminants they are meant to catch.
If the pre-filters are changed regularly, the membrane will last a lot longer. Membranes are flushing filters designed, to pass the contaminants they trap, down the drain while, sending contaminant free water to a storage tank. By testing the TDS level Of the incoming, unfiltered water, against the TDS reading of the filtered water from the membrane, you can determine the membranes rejection rate. An inexpensive TDS meter will give you the ability to see if the membrane is working or not.
If your RO unit is older than 5 years, consider replacing the entire unit. Most Ro units are made from plastic and most of them contain rubber o-rings. Over time an RO made of plastic can become contaminated and no matter how well it is cleaned or sterilized, it never really gets 100 percent cleaned out. To make sure you always have clean drinking water, replace the whole thing every five years. 4 stage RO systems are as low as $265.00 and in most cases this price includes installation.