The deionization process captures mineral ions — including cations like sodium, calcium, iron, and copper, and anions such as chloride and sulfate — that RO filtration cannot remove.  This process removes nearly all minerals, and is often used as final stage treatment for pure and ultrapure waters.

There are several different deionization systems. Service deionization (SDI) uses synthetic resins to remove ions. Electrodeionization (EDI) systems offer continuous deionization, since they use DC current to continuously regenerates the synthetic resins. Deionization units can also be combined with RO units into a single system.



  • Required flow rates and final water quality requirements,
  • Sizing, and materials of construction, including piping



  • ‘Polishing’ water from RO units to increase water resistivity and lower conductivity



Do I need to exchange or regenerate a deionization system offsite?  SDI units require offsite deionization.  EDI units do not require regeneration or exchange, since the regenerate the resins inside the unit

Are there any uses for deionization besides RO polish? Yes, in some cases EDI continuous deionization can be used to reduce/reuse waste water produced by an RO system by up to 85%.

What things do I look for if my continuous deionization system isn’t running well? Review DC voltage and amperage, look at pressure drops and flow rates. Reading outside the normal range for either will give you valuable information about the source of the problem.

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