[mike31154]

Water throughput as opposed to monthly or date driven regimen is the key. I keep track of water through my RODI with an Excel spreadsheet. Also have two pressure gauges to keep track of difference between input pressure & pressure after pre stages, before RO membrane. Aside from visual indication if your system has clear housings, the pressure differential is a reliable way of determining the condition of sediment filters.

Throughput info also provides an indication of when the carbon filter is nearing exhaustion. It would be a waste to change my 20,000 gallon 0.5 micron carbon filter every 6 months if I'm only putting 500 gallons thru the system during that time. Need to be aware that throughput calculation includes the waste water & any flushing as well as the half gallon dumped out at the start of production to get the TDS down to a reasonable number. So thruput formula would be gallons produced x 4 (assuming 4 waste to 1 good ratio) + gallons produced. In this scenario, 10 gallons of RO or RODI water produced would mean total thruput of 50 gallons.

You guys & gals on the west coast are fortunate to have relatively low TDS out of the tap. Here in the Okanagan, my tap TDS is over 200. Even so, I'm still on the original RO membrane & just recently changed out my carbon block after running the system since April 2009 having put just over 15,000 gallons thru. Could have pushed on for another 5,000 gallons, but preferred to err on the safe side. That's three and a half years on the same carbon filter. A swimming pool test strip kit comes in handy to check for chlorine after the carbon block if you really want to be sure the carbon filter is still good.

I run two sediment filters, a 5 micron followed by a 1 micron. The 5 micron needs changing every 200 gallons or so, the 1 micron is good for much longer. Time of year also has an impact as well as water temperature, run off & if the city happens to be flushing the lines in your neighbourhood. One pro about our water source out of Kalamalka Lake is that it's quite consistent.