Iron-electrocoagulation (Fe-EC), the electrochemical generation of Fe adsorbents in situ, is an effective treatment solution for arsenic (As) contaminated water in decentralized areas. However, extended field trials also revealed problems regarding the efficiency over long-term operation. To investigate how Fe generation is affected by repeated operation of Fe-EC systems, we performed laboratory experiments over a range of electrochemical and solution chemical conditions for 15–35 runs in batch mode. Our results show that Fe generation declines continuously during repeated operation under typical field conditions, resulting in a lower Fe dose than expected based on Faraday’s law. In addition, we find that efficient Fe generation can be maintained in electrolytes free of oxyanions or by applying charge dosage rates ≥15 C L−1 min−1. Based on these results, we discuss potential strategies to maintain the efficiency of Fe-EC field systems under realistic conditions.