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Arsenic III in water

How to Treat Arsenic III in Water


In our mission to explore the nuances behind arsenic contamination in water, we zero in on the two most prominent forms of arsenic in drinking water: arsenic III and arsenic V. Knowing their relative concentrations in your drinking water is critical for determining the optimal treatment technology for proper arsenic removal.  

NOTE: We look into the specifics of arsenic V in this article here. We suggest you review that article to read further details about the difference between arsenic III and arsenic V.

Now we focus on arsenic III, specifically:

  • What exactly is arsenic III?
  • Where do you find high levels of arsenic III in tap water?
  • How to test for arsenic in drinking water?
  • How to treat arsenic III in drinking water?
  • What Is Arsenic III and How Does It Differ from Other Forms of Arsenic?

    Arsenic III is one of the most soluble and prevalent forms of arsenic in groundwater and is often written interchangeably as arsenite, arsenic 3, or “trivalent arsenic”.

    Arsenite = arsenic 3 = trivalent arsenic

    Arsenic III is a form of inorganic arsenic, which is known to be highly toxic in comparison to organic arsenic, which is considered relatively harmless.  

    Arsenic III is the most toxic and bioreactive form of inorganic arsenic in drinking water. Unfortunately, it’s also particularly difficult to filter out.

    Why Do Some Waters Have High Arsenic III to Arsenic V?

    You’re more likely to find arsenite in reduced well waters rather than city water. Note: most city or community water systems will treat or mix water to remove total arsenic to at least below the EPA MCL of 10 parts per billion (PPB). However, if water is treated with free chlorine then you probably don’t have high levels of arsenic III in your tap because chlorine rapidly oxidizes arsenic III to arsenic V.

    The only way to know your arsenic 3 concentration (and your arsenic 5 concentration) is to run a water test in an environmental testing lab.

    How to Test for Arsenic in Water at Home?

    Firstly, if you are concerned whether you have any form of arsenic in your drinking water, the best thing is to test for the total amount of arsenic in your water. Tap Score’s city testing and well water testing packages test for total arsenic, as well as a wide array of toxic metals, harmful chemicals, and physical parameters that you’ll want to know about.

    If you find that you have high arsenic levels in your water, and you want to most effectively remove it, then the necessary follow-up step would be to determine how much of your total arsenic is arsenic 3 vs arsenic 5. Although the information explained above might point you in the right direction in understanding your arsenic makeup, an Arsenic Speciation Water Test is the only way to know. Once you know your arsenic 3 vs arsenic 5 balance, then you can then reliably pick the best treatment system for your water and effectively remove arsenic from your tap. 

    How to Remove Arsenic III From Water?

    Arsenic III is much more difficult to remove than arsenic V by both conventional and unconventional treatment methods. There are two ways to treat arsenite in tap water:

  • Pre-treatment, OR
  • Using a specialized treatment method that targets arsenic III (like distillation or specialized iron adsorption (granular ferric hydroxide) media)
    • The surest way to remove arsenite from your water is by applying a pre-treatment method that oxidizes arsenic III to arsenic V. Following such pre-treatment, you can then effectively remove (both forms of) arsenic with reverse osmosis or certain types of filtration

      Another way to remove arsenic III from your tap is by distillation, which requires no pretreatment. Distillation treatment systems remove nearly all metals by heating the water, collecting the steam and cooling it back to precipitation as “treated” clean water.

      Contact Tap Score

      Still have questions? The good news is you have a few options:  

    • Check out this Tips For Taps article on arsenic V, it provides extra information on the different types of arsenic species in drinking water.
    • Send a message to Tap Score’s team of scientists, engineers, and water experts at about any water quality question you might have.

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