What causes EDI product water resistivity to decline and how should it be troubleshooted?

A decline in EDI product water resistivity is typically caused by poor feedwater quality, membrane fouling, inadequate feed flow, or unstable power supply. EDI systems are designed as a final polishing step after reverse osmosis and require stable, low-TDS permeate as input. If resistivity drops, first verify the quality of the RO permeate—elevated TDS or residual oxidants can degrade EDI performance. Check that feed flow matches system design specifications, confirm DC power settings are within recommended ranges, and inspect the concentrate stream for scaling or biofilm accumulation. EDI systems should include real-time resistivity monitoring and alarms to detect deviations early. Do not exceed manufacturer-specified voltage limits to avoid irreversible module damage. If issues persist, evaluate upstream pretreatment and RO performance, as EDI cannot compensate for inadequate feedwater quality. Regular maintenance of pretreatment components and periodic system validation are essential for sustained performance. EDI troubleshooting requires a holistic review of the entire water purification train, not isolated module adjustments.