a method and apparatus for detecting contaminants in an aqueous flow . the method includes the steps of providing a conduit having at least one collection portion upon which is disposed a selective film , disposing the aqueous flow through the conduit , attracting contaminants to the collection portion such that they are bonded to the selective film , and detecting a contaminant , or contaminants , based upon a predetermined property of the plurality of contaminants bonded to the ion collection portion . the selective film may include a molecularly imprinted polymer , a crown ether , an antibody selective for biological contaminants , such as giardia lamblia and cryptosporidia , or for detecting organics such as dioxin or furan , a cyclodextrin , or a cyclophane . the apparatus includes a conduit having an collection portion with a selective film disposed thereon , a sensor that senses contaminants collected on the collection portion and sends a signal corresponding to a value of a predetermined property of the contaminants , and a microprocessor in communication with the sensor and programmed to process the signal and determine the presence of contaminant based upon the processed signal .