We've had our 4040 ro since August 2012.
We're a 2 man set up using 500-600 litres per day.
So we've been using it for 18 months totalling around 306 days ( full days )
My water measures 185 from the tap so not too hard really
I checked the tds yesterday and its reading 29. rechecked it several times and still around the 29 mark.
After 18 months should we need to replace the membrane ?