Hi again Mr Proff
Here's what my costing on a meter up here would be with your magic contraption if I had an input of 100 TDS
£6.20 per 1000 at present with just the DI
£2.90 per 1000 at 10 tds through the Merlin including waste at 1 to 1 ratio of waste to RO output to DI
So a saving of £3.30 per 1000 ltrs.
In my case at a usual daily usage of 500 ltrs it would take me 200 working days or so to justify the Merlin.
Personally I would go for a 2 or 300 GPD RO MAN unit though because I get my TDS down from 415 to 9 or 10. So you should get yours down to 3 or 4.
Of course it depends on how much and how quickly you want to be able to produce water.
Actually if I were you I wouldnt bother with a RO bearing in mind how much each 1000 ltrs can make you but one would pay for itself well within a year. PS havent included the price of replacement membranes coz I cant be bothered :
Andrew