USA EPA (Environmental Protection Agency)in December 2000, has established a maximum contaminant level (MCL) for uranium of 30 micrograms per liter (µg/L) in drinking water. The MCL is the maximum permissible level of a contaminant in water that is delivered to any user of a public water system. Because it is for drinking water, i.e. a direct exposure to human body, I believe any country or community could use this limit as a guide.

You can follow other acceptable global standards for contaminants and elements in the drinking and potable water such as WHO (2004), US-EPA, EU-EPA, Canadian EPA and many others.

did you try to find uranium orebody from hydrochemical data ?