41400009 Hydrotech Reverse Osmosis FilterThe Hydrotech 41400009 replacement carbon pre post filter effectively removes chlorine taste and odor and particulates to protect the more expensive filters in your system. An activated carbon pre filter is required if you are using a TFC membrane to prevent fouling, and is also used as a polishing filter to improve taste. If you're not getting enough product water you should replace the pre filter cartridges to maintain optimal system performance.