Honestly, we had not pondered that question… until now. Though we checked only one site, it appears as though one may want to do their homework before investing in a commercial reverse osmosis water filter if pinching pennies matters because the RO membranes in the 4,000 gallons per day unit we brought to everyone’s attention uses 4″x40″ filters that cost no less than $290 apiece on the various sites we checked.

We suppose, however, that anyone willing and ready to drop around $5,000 on a high volume water filtration system probably expects to spend a few bucks on the unit’s replacement RO membranes

Thankfully, though, replacement reverse osmosis membrane prices for point-of-use systems for households, small businesses, etc. still cost in the range of $100 or so.

Now that we’ve done a little research, we can definitely say that anyone considering purchasing a reverse osmosis unit should make sure the unit they want to purchase uses a universal size of ro membrane — else face really high replacement costs and/or the risk of not being able to find a replacement at all!

“Overview: This standard was developed for point-of-use (POU) reverse osmosis (RO) treatment systems. These systems typically consist of a pre-filter, RO membrane, and post-filter. Standard 58 includes contaminant reduction claims commonly treated using RO, including fluoride, hexavalent and trivalent chromium, total dissolved solids, nitrates, etc. that may be present in public or private drinking water. (source)