Single-pass RO typically delivers 50–200 µS/cm. Double-pass brings that to 1–5 µS/cm. The question is whether you need it.

Choose double pass when

  • You need conductivity below 10 µS/cm without EDI
  • Silica or boron limits are tight
  • Feed water quality fluctuates seasonally
  • You have a pharmacopoeia or electronics specification

Stay single pass when

  • Boiler make-up or general process water is the duty
  • You will polish with EDI anyway — EDI handles the last 95% more cheaply
  • Floor space is very tight

A useful rule: if your target is under 10 µS/cm and EDI is not in the budget, double pass is usually the right answer.