Sounds like a good place to consider a well into a deep aquifer away from the toxics, or installing a pipe in the headwaters or upstream away from heavy pollutants.  Sorry, I am not a toxicologist if that is what you are looking for, but if they cannot find other sources, at least consider some extra filtration system for drinking and cooking as a minimum.  I am not up to speed on these survivalist hand held filtering apparatus that individuals may used to filter out water before they boil it and drink.  If you are in an area with well distributed rain, you might be able to capture it from roofs for a better quality water source with less treatment needs than what you describe.  Stream water can have all sorts of other pollutants, bacteria, etc. that affect health.  The take ocean water and distill it, boiling then condensing the vapor and collecting the distilled water.  Distilled water is not necessarily the healthiest to drink.  Activated charcoal can pull out some types of contaminant.  Hopefully this paper I attached may give you some ideas relative to drinking water from forests and grasslands.  I have seen on survival program how in some places they find coconut, bamboo or other plants that collect and store liquids that are drinkable.  Sometimes you might use aquatic insects as water quality indicators, as some are pollution intolerant and some tolerate a certain degree of pollution. If the river contain pollution intolerant aquatic insects (you need a key to species in your area), it suggests the conditions may not be so bad.  But the river source may be a reliable source relative to quantity, but not quality.  Anytime inhabitants see fish or aquatic organisms stressed or floating, they should avoid all contact.  Swimming and bathing in polluted waters is not ideal and could also a problem as some pollutants absorb through the skin.  For some pollutant types, high water stormflows provide more dilution, but also many more potential for contaminants washed off the land or failed systems. Researchgate may have a toxicology section, but you need to have some idea of the contaminants, ahd if possible the frequency, duration, severity.  A geologist may be able to review formations and estimate if you might have suitable groundwater sources such as from a confined aquifer.    

Thank you  very much Prof Hansen, I really appreciate