Is there a DI calculator to work out the cost of producing 1 ltr of  pure water using DI only?
  Something like:
TDS In
Litres used per week / month
Resin used per month etc
Giving cost of purifying  1 ltr
I ask as my RO tds readings are going up but I have reduced my work load over last 2 years and now work just 10 hours a week using about 600 lirs of pure.  I will be stopping in 3 years
I'm not sure if its worth buying a new RO or just keeping the old one and as TDS goes up just use more resin?
Any calculators about??