How to Remove Arsenic from Well Water

Arsenic is a toxic metal that’s naturally found in some soil and well water. Local industrial or mining activity can raise the levels of arsenic in well water.

When consumed in quantities above EPA safe limits (currently set 10 micrograms per liter), arsenic can cause nausea, diarrhea, and skin complaints.

If large quantities of arsenic are consumed over extended periods, the metal may cause chronic and serious diseases such as cancers or liver failure.

Because arsenic has no smell or taste, it can be present in well water that appears perfectly safe to drink.

To remove arsenic from well water, well owners should employ one or more relevant filtration stages.

Illustration of Arsenic element with water droplets

This page details the most common filtration stages for arsenic removal, including their relative strengths and weaknesses.

Treatment techniques for reducing arsenic to safe levels in well water include:

  • Reverse osmosis filtration
  • KDF filtration

Reverse osmosis filtration

The most commonly recommended treatment method for arsenic in well water is reverse osmosis (RO) filtration. Reverse osmosis filters for well water are used in both industrial and home settings to remove a wide range of contaminants from drinking water, including metals like arsenic, chemicals, sediment, and microorganisms.

RO filters consist of a series of micro-pore membranes—semi-permeable screens with microscopic pores, so small that they provide filtration on a molecular level. To push water molecules through these membranes, RO filters may also contain pumps to increase well water pressure.

Other components of RO filters include additional carbon filtration stages to remove any residual traces of dissolved chemicals. Because the RO filtration process can significantly lower the water flow rate, systems may also contain water storage tanks that allow the filter to build up a reserve of water.

Should I use a Reverse osmosis system to remove arsenic from my well water?

Consider using a reverse osmosis system for well water when:

  • You're looking for the most common and widely accepted arsenic filtration option
  • You need a wide-ranging filtration solution that also reduces levels of other metals, chemicals, and microorganisms
  • You're looking to remove arsenic in water coming from a single faucet or fixture (with an under-sink filter)
  • You're purchasing a reverse osmosis filter alongside a water storage tank so that the flow rate to your home isn't compromised.

Think about other options instead of reverse osmosis systems for well water if:

  1. You're not installing a water storage tank and you can't accommodate any flow restriction
  2. You want to retain your well water's mineral content
  3. Your well water has high sediment levels and you don't also install a micron filter

What about KDF filters?

KDF filters are an increasingly popular type of cartridge filter that can be used to remove small-to-moderate levels of arsenic from well water.

These filters use a granulated media made of a copper-zinc alloy that reacts with certain dissolved metals in a water supply. This reaction causes an oxidizing effect, which results in the metal contaminants becoming insoluble. This allows the filtration system to easily extract arsenic and other metals using a traditional screening stage.

While the treatment method employed by KDF filters is suitable for arsenic filtering, these devices tend to possess a lower performance rating and capacity than reverse osmosis filters.

KDF filters also become inactive when their cartridges are saturated with contamination. This means that users need to proactively monitor and replace filtration cartridges to avoid arsenic from reentering their water supply.


What about ion-exchange filters (water softeners)?

Some websites recommend using an ion-exchange water filter to remove arsenic. This advice can be misleading.

Ion-exchange water filters are more commonly referred to as water softeners. In the majority of cases, these devices are designed to soften water by reducing levels of hard minerals such as calcium carbonate and magnesium that are commonly found in US well water.

Well water softeners achieve this effect by exposing water to a charged resin bed filled with salt ions. Mineral ions in the water supply are attracted to the resin bed and exchange places with salt ions, leaving the water supply.

A small number of ion-exchange systems are designed with a specialist resin bed and use a particular kind of salt that allows them to attract and remove arsenic ions. However, these devices are rarely sold by large water filtration or home product stores.

Traditional water filters can still be useful in arsenic removal systems, as removing high levels of hard minerals from the water supply increases the effectiveness of reverse osmosis and/or KDF filtration.

Consider using an ion exchange system for well water when:

  • You already have an arsenic filter installed and you're looking to boost its effectiveness.
  • You understand the difference between a traditional water softener and a softener system designed to additionally remove metals such as arsenic

Think about other options instead of an ion exchange system for well water if:

  • An ion exchange filter will be the only stage in your filtration system

You cannot remove arsenic from well water by:

  • Heating or boiling your water. basic methods of water treatment such as boiling are not appropriate for removing dissolved metals such as arsenic.
  • Chlorine (bleach) disinfection. Chlorine is the most common method of reducing drinking water risks from microorganisms and some chemicals. However, it will not affect arsenic levels.
  • UV purification. UV irradiation is another effective method of disinfecting drink water to reduce pathogen health risks. Again, however, it has no effect on arsenic.
  • Carbon filtration. Carbon filters are the most common type of home water treatment device. While large GAC carbon filters may reduce minimal amounts of arsenic, they should not be considered an effective arsenic removal method.