Please have a look at these links and PDF attachments.

https://www.researchgate.net/publication/287811701_Fluoride_and_Nitrate_Groundwater_Contamination_in_Rajasthan_India_A_Review

https://www.researchgate.net/publication/280999554_Arsenic_and_fluoride_contaminated_groundwaters_A_review_of_current_technologies_for_contaminants_removal

https://www.researchgate.net/publication/281865761_Groundwater_Arsenic_Contamination_in_Bihar_Causes_Issues_and_Challenges

https://www.researchgate.net/publication/225809933_Assessment_of_Ground_Water_Quality_for_Drinking_Purpose_District_Nainital_Uttarakhand_India

Conference Paper Fluoride and Nitrate Groundwater Contamination in Rajasthan,...

Article Arsenic and fluoride contaminated groundwaters: A review of ...

Article Groundwater Arsenic Contamination in Bihar: Causes, Issues a...

Article Assessment of Ground Water Quality for Drinking Purpose, Dis...

Dear Mr Ba

Contaminant is a term generally used for a chemical substance (natural or artificial) which is present in higher level than their natural background in the environment, and that could induce a risk for the ecosystem. Thus, you can have many contaminants in the water, including organic (PHA, PCB, pesticide, ...) and inorganic (metal, radionuclides...) substances. They will be present depending on their sources.

Source of well water is usually from groundwater which can contain inorganic (Nitrate-as nitrogen, Nitrite-combined nitrate/nitrite, Aluminum, Antimony, Arsenic, Barium, Beryllium, Cadmium, Chloride, Chromium, Copper, Cyanide, Fluoride, Nickel etc) and organic contaminants such as pesticides, PAHs, volatile organic compound  etc. Sources of contaminant are natural or human made. Many articles are available.................

No, many contaminants can be found in the ground water according to the area and for example of you have land fill you can find many time of pollutants in your ground water .

 So it depends on your location and source of your well water