as long as your tap pressure is over 40psi then it will make more than most will ever need. we still have ours (it feeds the spare tanks at my sons), most of the time we fill up at mine (twin 4040 boosted) but only because of convenience (I've a bigger yard for the vans etc)
at my sons the tap pressure is 50psi and it will make about 1500ltrs a day there, tap tds in 215ppm, out 007ppm.
there's a carbon prefilter in them but we binned it and use a 10inch sediment and a 10inch carbon before the merlin, the top sump is obviously empty then.
good little system, before the 4040 it was at my yard and we use about 1000ltrs a day so over the 2 years at my yard it prob made around 400k - 500k litres, still going good.