my last membraine it was producing 005 for the first eight months, when I got a little lazy and left the carbon filter for 3 months the tds started to rise, even after changing the carbon filter it then kept going up until I had to change the membraine at 040 - I think the carbon filter expired allowing chorine contamination.
I produce at least 10k pure per week, so that's 20k through the filters, it should mounts up
Darran