Observation of arsenic water treatment adsorption media in the treated water of several homes with high arsenic private wells led to the hypothesis that treatment media was escaping the treatment systems and entering the plumbing and drinking water. Our research at 62 homes identified that microparticles of arsenic water treatment media and/or water softener resin had escaped the treatment system in 71% of the homes. This is a potential health hazard as ingesting arsenic treatment media or water softener resin may lead to an elevated ingestion exposure to arsenic and other contaminants. Potential causes of media escape from the treatment systems include media observed to be smaller in size than specifications and media breaking into smaller pieces. One interim solution to media escape is installation of a post‐treatment sediment filter. New developments in media durability or treatment system design and maintenance may be needed to prevent media escaping into drinking water. Practitioner Points Arsenic in private wells is often treated with point‐of‐entry whole house adsorption systems. Arsenic adsorption treatment media and/or water softener resin was observed in treated water at 44 of 62 homes inspected. Water treatment media escaping into treated water is a potential hazardous exposure pathway. Potential causes and solutions are discussed. Investigation at 62 homes with high arsenic private wells identified that microparticles of arsenic water treatment media and/or water softener resin had escaped the treatment system and entered drinking water in 71% of the homes. Ingestion of these microparticles may lead to an elevated exposure to arsenic and other contaminants.