Chlorine will wreck a reverse osmosis membrane.
It's in the water coming out of every tap in the UK. Its purpose is to kill organisms that would otherwise breed in the water supply and to prevent out breaks of such delightful diseases as cholera. So it's a good thing.
However, it does destroy RO membranes. Slowly but surely. So you need to get it out of the water before it gets to the membrane. To do this you need some kind of carbon filter that absorbs the chlorine. The problem is , that's just what charcoal does, absorb. It doesn't convert it into anything else, just slowly soaks it up. Then a point arrives where the charcoal can take no more and the chlorine in the water passes straight through and starts eating away at the membrane. Your output TDS starts to creep up. If at that point you replace the carbon filter no more damage will be done but equally your membrane won't recover and you'll be using more resin for the rest of your time with that membrane.
So you need to replace a charcoal filter
before chlorine starts to get through. Which means sticking to the manufacturer's recommendations - a filter should say how many litres it can take before saturation. However, that's based on a degree of guesswork abut how much chlorine there is in the water coming out of
your tap. It's probably pessimistic and can in many circumstances be stretched. However, the cost if you're wrong is a new membrane (for a 4040, the thick end of £250).
So, if you don't want to be measuring water use every day and tracking against the recommended life of the block, what's the solution?
We use a spectrum DI vessel full of acid washed charcoal. It's all from Gaps Water and the vessel and enough charcoal to last about three years will set you back about £75 (vessel) plus £140 (charcoal). Then the running costs will be about £50 worth of charcoal a year. That's based on a similar usage to you.
We do still have a particle filter after the charcoal but mine's picked up nothing at all in two years - it still looks brand new - which suggests the charcoal is also filtering out particles. When I used the old prefilter system they used to end up deep brown (see pic below) but now it's still white after 24 months. I'm going to drop the particle filter on my annual charcoal change in May. The guys all use a 20"x8" Spectrum vessel and an annual change does the job. That's cheaper than the amount you'll spend on 20" filters plus we only have an annual ten minute change to do.
Hope that helps,
Vin
