An R/O membrane is like an air filter in your car or van engine's air intake.
The airfiter is made of a porous material that has tiny holes in it that allow air through but not dirt. So we have to change our airfilters regularly as they eventually get clogged up with the dirt they have trapped.
An R/O membrane does the same as it stops the impurities in the water passing through it like calcium and magnesium. So water molecules can pass through this membrane but impurities can’t. R/O’s have an added feature of having some water wash over those membranes which helps to keep the membrane’s surface clean. This is the waste water we talk about.
But some impurities are so small that they do pass through the membrane and we then use resin to remove those minute amounts.
Our 4040 r/o membrane brings our tap water ppm down from 115 to about 2ppm. We can clean windows at 2ppm but we choose to put it through a resin di vessel to ‘polish’ it off to zero.
I am interested in this thread too. Thanks for explanation. Just wondered what the three pre filters before my ro do. My tap tds is about 350 and my filters are about a year old now but I only filter about 400l of pure a week. Are they due a change.
The pre filters are there to protect the R.O. without them it wouldn't last long.
You will have as follows.
Sediment filter....This filters out dirt and sand which would quickly clog the R.O.
Carbon block.....This removes chlorine which destroys R.O. membranes very quickly.
GAC filter........ This protects against higher levels of chlorine.
They all have a lifespan measured in the amount of litres of water which can pass through them before
needing changed. This will depend on the make of filter you buy.
Im not sure on this one but there might be a time limit on them from when they first get used.
I personally wouldn't let them go a year without changing.