How Often Do I Change My RO Filters?

We have dealt with this question a few times before but some new information has surfaced that might be of help to the average residential reverse osmosis user and industrial/commercial user as well.

Most industrial/commercial reverse osmosis (RO) systems are very high performance and high capacity. Any of the commercial RO systems we sell come with monitors that provide real-time read-outs of the input and output water states. The most accurate and convienient method of monitoring the input (feed) water and output (product) water of a reverse osmosis system is through the measurement of Total Dissolved Solids (TDS).

TDS is easily measured by running a low voltage current through the water and determining the amount of resistance compared to the temperature of the water. The higher the resistance, the more TDS the water contains.

Reverse osmosis systems are designed to remove all dissolved solids from your water, so if a measured reading is over 50 parts per million (ppm) of TDS, then there is either a filter or membrane that needs your attention. We use the value of 50ppm as a guidline as that is the average reading of randomly sampled commercial bottled water product results. Once your RO system exceeds 50ppm, you might as well be paying top dollar for your drinking water at the local market, OR you can opt to treat your body to better-than-bottled-water by replacing the sediment pre-filter in your RO system.

Once your sediment pre-filter is replaced, you can expect TDS readings of 0 to 35ppm. If your readings are greater than 35ppm then you probably need to replace the carbon filter in your reverse osmosis system as well. Just like the sediment pre-filter, the carbon filter is designed to protect the RO membrane in your drinking water system. If you have kept up with your sediment pre-filter changes then you can expect to replace the carbon filter about every 8 to 12 months of regular use.

So what happens when you change both the sediment and carbon filters and your TDS is still pushing 50ppm? Then it's time to replace the membrane. A typical thin film composit (TFC) membrane should last 3 to 4 years in your RO system so long as you keep up with the sediment and carbon filter changes. The typical RO membrane is several times more expensive than the sediment and carbon filters so keeping up with filter replacement is directly proportional to the expected life time of your reverse osmosis membrane. The most accurate method of monitoring your RO water input and output is through the use of a TDS monitor.

There are two types of TDS meters that are readily available. The handy "pocket TDS" monitor and the "inline" style. The advantage to the pocket TDS monitor is that it is portable and can be used at numerous locations. The typical "inline" TDS monitor is by far the best for commercial/residential reverse osmosis systems. With the press of a single button and the flick of a switch, the prformance of your reverse osmosis system can be realized accurately. There is no need to estimate the efficiency of your RO sediment or carbon filters. Simply look at the output of your TDS meter. In the long run, an inline TDS monitor can save you several dollars per year and the even greater expense of replacing your RO membrane. With proper filter changes, your RO membrane should last 3 to 4 years.

Find out more about TDS meters here.