Biological and chemical contamination of natural water bodies is a global health risk for more than one billion people, mostly living in low-income countries. Innovative, affordable, and efficient decentralized solutions for safe drinking water supply are urgently needed. Metallic iron (Fe0)-based filtration systems have been described as such an appropriate solution. This communication focuses on the Kanchan arsenic filter (KAF), presented in the early 2000s and widely assessed during the past decade. The KAF contains iron nails as the Fe0 source and is primarily designed to remove As from polluted tube well waters. Recent independent works assessing their performance have all reported on a high degree of variability in efficiency depending mostly on the following factors: (1) the current operating conditions, (2) the design, and (3) the groundwater chemistry. This communication shows that the major problems of the KAF are two-fold: (1) a design mistake as the Fe0 units disturb the operation and functionality of the biosand filter, and (2) the use of poorly characterized iron nails of unknown reactivity. This assertion is supported by the evidence that the very successful community filter designed by the Indian Institute of Technology Bombay works with iron nails and has been efficient for many years. Replacing iron nails by more reactive Fe0 materials (e.g., iron fillings and steel wool) should be tested in a new generation KAF. It is concluded that a methodological or systematic approach in introducing and monitoring the efficiency of KAF should be used to test and disseminate the next generation KAF worldwide. Moreover, better characterization of the Fe0 materials including their intrinsic reactivity is required.