How would I know if my water has elevated arsenic?

 
Arsenic in water is tasteless and odorless, so water must be tested to determine if the arsenic concentration is elevated.

In Ohio, iron staining is an indication that well water might contain elevated arsenic. more

Iron staining is caused by elevated iron concentrations. Elevated concentrations of arsenic and iron often occur together, since the same geochemical conditions that cause arsenic to be released from rocks and soil also cause iron to be released. However, not all groundwater with elevated iron also has elevated arsenic.

Arsenic should be less of a concern to people who get their water from public water systems than from private wells.  (Private wells include household wells and wells that serve small businesses or public facilities).
Private wells are not typically tested for arsenic.  When a private well is drilled (or an existing well is altered), the local health department tests the water for bacteria and nitrate, which could indicate contamination by septic systems, manure, or fertilizer.
It is the responsibility of the private well owner to have their water tested for arsenic or other contaminants. To get water from a private well tested for arsenic, contact your local health department or a certified lab:

Public water systems are periodically tested for arsenic and other constituents, and the results are reviewed by the Ohio EPA. Water from public-supply wells is required to meet health standards, so it may be treated before being distributed to the public.
Test results for city and village water systems are reported in Consumer Confidence Reports, which are sent to customers each year.

Public water systems that do not meet USEPA health standards are listed at http://wwwapp.epa.ohio.gov/ddagw/Advisories/advisories.html.

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