Is there any way to determine which arsenic species is in my water (Arsenic 3 or Arsenic 5)?
There is no simple and affordable test commercially available to determine which arsenic species is present so the species of arsenic present is usually unknown.
There is an Arsenic Speciation "Rule of Thumb" developed by the New Jersey Geological and Water Survey and Rutgers University that can be used to determine if Arsenic 3 may be a factor or not.
The Arsenic Speciation Rule of Thumb works by answering these two questions:
Are the Iron or Manganese concentrations in the untreated well water greater than 50 micrograms/liter (mcg/L)?
Is the Dissolved Oxygen concentration in the untreated well water less than 1.0 milligrams/liter (mg/L)?
If the answer to each question is "no" it is very unlikely that the water contains a significant concentration of Arsenic 3.
If the answer to either question is "yes" then Arsenic 3 is likely present at a concentration greater than 3 mcg/L and therefore a serious factor in water treatment selection. In this case, a confirmatory Arsenic 3 test by arsenic speciation cartridge or laboratory analysis is recommended before spending extra money on treatment components to convert Arsenic 3 to Arsenic 5.