As mentioned before, I recently bought a 4021 RO, with sediment and carbon filter. This whole purification thing is starting to drive me crazy to be honest. First time I assembled the system, I got 015ppm coming out from pure. After producing maybe a 1000L it's reading 025 now.. The pressure gauge shows 45-50psi before and 30psi after prefilters. After the first 1000 litres pressure dropped, so I had to change the sediment filter. Will I have to change the sediment filter every other week?! And what's going on with the tds? If it's going up with such rate, I will have to buy a new membrane sooner than I thought. The other strange thing is, when I measure how much waste and pure is coming out, in 10 seconds it's something like 300ml (100ml pure to 200ml waste), in one minute that's only like 2 litres altogether? spruce you say your 4040 does 2 litres of pure in 1 minute! Something doesn't add up here.