Yes, and filters take careful watching and regular replacement or cleaning, or they can become not only ineffective but more dangerous. They can build up a biofilm of organics that metals bind to, and can reach the stage where they are clogged enough that the flow speeds up in only a part of the filter, where pieces of the metal-contaminated biofilm come off episodically. This can cause a higher dose that has accumulated from low dose water. Whoever is the unlucky one that happens to drink that can have a much higher dose delivered. I'll bet that there was pretty lax care taken of those filters.