In San Antonio, many houses have Reverse Osmosis Systems (RO), and Water Softeners. However, many people do not know the best timing when their filters must be replaced. In this article, I want to mention the timing of filter replacement while touching on the features of both devices.


First, let me touch on the features of both devices briefly. Water Softener removes calcium and magnesium and releases sodium in water. Reverse Osmosis System purifies water molecules and removes all particles in water.


Therefore, as mentioned in the past in this blog, water softeners do not purify water at all.


Let’s see the difference between both devices.

Water Softener vs RO Chart

Reverse Osmosis Systems are designed to make drinking water. As TDS in the chart shows, calcium and magnesium causing lime scales, chlorine causing odd, and all particles are removed by Reverse Osmosis Systems.


On the other hand, Reverse Osmosis Systems cannot produce large volumes of purified water. To solve this issue, purified water is stored in its separated tank. The purified water is dispensed from the tank, so a sufficient amount of water is dispensed to use. Also, when the tank gets full, making purified water stops automatically with its water pressure valve.


Reverse Osmosis Systems consist of mainly 4 filters. They are sediment, pre-carbon, membrane, and post-carbon (Inline) filters. Let’s see each detail.

Reverse Osmosis Image

Sediment filters trap dirt particles with a bed of media made of main polypropylene.


Sediment cannot remove trace pathogen elements, heavy metals, and volatile organic compounds from water. In general, the sediment is equipped at the first stage of Reverse Osmosis Systems


Pre-carbon filters remove chlorine, volatile organic compounds (VOCs), and so on while adsorbing them. The chlorine and VOCs cause odd. It is located in the second stage.


The membrane is the key part of Reverse Osmosis Systems. The membrane has very small pores and only H2O molecules can pass through the pores. This is the reason why water is purified. On the other hand, dirt water is made simultaneously while purifying water and it is almost the same amount as the purified water. The dirt water drained from another hose of the Reverse Osmosis Systems. It is located at the third stage.

Membrane Image

Post-Carbon filters are located at the end of the Reverse Osmosis System. It works for odd and taste of water. It is located at the final stage.


The timing of filter replacement varies by public water’s quality. So, it can be said that the timing of replacement for sediment, pre-carbon, and post-carbon filters is its clogging inside. However, unfortunately, we cannot see inside so it is better to replace filters following the description written on each filter.


On the other hand, membrane performance can be measured by TDS meter. TDS meter can detect how many inorganic ion particles are in the water. So, if the TDS detects more than 75 ppm, it is the timing to replace the membrane.

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