Input TDS 300-330 here, output 004. 500L a day, three days a week. My setup is:
Pump
30" Spectrum DI vessel 2/3 full of acid washed charcoal*. I am reliably told (June at Gaps) that this is sufficient as a particulate filter as well as a chlorine filter. I went to this because occasionally our water tastes earthy (surprisingly pleasant) then, the following day, like a swimming pool.
Particulate filter - despite the charcoal being acid washed some bits of carbon do wash out of it initially. The filter is there to catch them before they hit the membrane. My filters used to come out dark brown*** and they now come out with a faint tinge of grey from the charcoal. That suggests the charcoal is collecting crud as June suggested it would.
RO. I've never used a water softener which is probably why I only** got seven or eight years (I really can't remember but it's there or thereabouts) out of my last membrane. And that was because my feed pipe had a split, sucked in soil and I had a biological fouling of the membrane. Before that it had crept up to 012TDS output, which I considered to be perfectly OK.
Vin
*Used to be £120 a bag, now £220 because it's become fashionable to eat it because it "removes toxins" from food in your stomach. I wish I was joking. I get three fills from a sack, each fill lasts a year.
** sarcasm
*** They used to look like this:
Poll