40000 litres under what conditions.
250 litres a day with tap water of 200 tds or 1000 litres a day with tap water of
400 tds. Also the closer you live to a water processing plant the higher the chlorine level.
Its all guess work and finding what works for you.
TDS cannot affect a particulate filter, as it can't remove anything dissolved, Not sure about charcoal on that front, though.
Chlorine levels depend on many things as well as distance from the plant, so it might be wise not to depend upon that alone.
My solution on the particle front has been to run two filters. As soon as number 2 shows
any sign of discolouration, it becomes number 1 and a fresh filter no 2 goes in. (Done that since - and as a result of - the pic above)
Vin