Meganoth is correct, IMO. If the dew collector gave murky water without a filter there'd be no point in getting a filter, *especially* if the filter would cost 250 polymers like you suggest. I'm not gonna spend 250 polymers just to save me the process of turning the murky water into water by simply boiling it in the campfire. That's not much effort at all, really.
EDIT: That said, I do like the idea of tools for the Dew Collector like other workstations. For example, a tool that adds more capacity to it, or increases its collection speed.