Perchlorate is a naturally occurring and man-made synthetic “anion” (negatively charged ion) commonly associated with the solid salts of ammonium, potassium, and sodium perchlorate. Synthetic perchlorate is used in the manufacture of fireworks, explosives, flares, ammunition, and rocket propellant.

What are the health risks from perchlorate?
Ingestion of perchlorate affects iodine uptake by the human thyroid and thus thyroidal hormone production. However, the public health risk from perchlorate remains controversial. The U.S. Environmental Protection Agency (USEPA) announced in 2011 its intention to regulate the allowable concentration of perchlorate in drinking water, though a federally designated maximum contaminant level has not yet been established.

Two states have mandated maximum contaminant levels for perchlorate: 6 micrograms per liter in California and 2 micrograms per liter in Massachusetts. Other states have guidelines ranging from 1 to 18 micrograms per liter.

Is my private well at risk?
Perchlorate contamination has been recognized in groundwater throughout the United States at sites where perchlorate has been manufactured, used, and stored. Many of these sites are associated with the military and aerospace industries where synthetic ammonium perchlorate has been used since the 1940s as a component of solid propellant fuels for rockets and missiles.

If a residential well is located in a region known to have this type of industrial activity, the groundwater may have been impacted. Also, some types of fertilizers have been linked to perchlorate presence. You can contact a local environmental regulatory agency or the USEPA to ask about industrial pollutants in soil and groundwater in your area.

Disinfection of wells using household bleach also could introduce perchlorate into groundwater. The level of perchlorate in bleach will increase as the bleach ages or is stored at elevated temperatures. The National Ground Water Association (NGWA) recommends that only disinfectants certified for use in drinking water be used to disinfect private household wells.

How do I test for perchlorate in my water?
At present, a limited number of drinking water testing labs test for perchlorate. To help you locate a lab that does, contact your state program involved in lab certification. Depending on which type of test is indicated, costs can run from about $125 to $225 for a test. Water samples should be taken only after a well is cleaned and suitable volumes of water have been pumped to make sure representative groundwater quality samples are collected. Sample collection should follow procedures provided by a qualified drinking water lab, which should do the water analysis.

How can I eliminate perchlorate in my drinking water?
The well owner has three basic choices for eliminating perchlorate in drinking water:

  • Explore with a qualified water well system professional the feasibility of retrofitting the well to block off the perchlorate-producing zones.
  • Build a new well system that isolates the likely perchlorate-producing zones of groundwater.
  • Install appropriate water treatment technology.
What types of water treatment are effective for perchlorate?
Before buying a water treatment system, well owners should have their test results from a qualified drinking water testing lab. Those results then should be compared to the specifications of the water treatment system under consideration to make sure the system is designed to treat the concentration of perchlorate indicated to acceptable levels.

Reverse osmosis (RO): This is a process for removing dissolved ions from water, in which water is forced through a semipermeable membrane, retaining most ions while transmitting the water. Some NSF-certified reverse osmosis technologies have reduced perchlorate levels from as high as 130 micrograms per liter down to 4 micrograms per liter or less.

Most RO units can be fouled by low concentrations of slightly soluble minerals such as calcium, magnesium, iron, and manganese—so some pretreatment of the water may be required.

With RO units installed at the point where water is being used, such as at the tap, a minimum of three gallons of wastewater is discharged for every gallon of treated water. Often the wastewater can be used for non-drinking purposes.

Maintenance of RO units involves replacement of pre- and post-filters as well as the membrane, which can last three years or more.

Ion exchange: This is a physical/chemical process in which ions are exchanged between a solution phase and a solid resin phase. An ion exchange system can be installed at the point of water use or where the water enters the house.

Pre-filtering of water using sediment filtration is recommended as a precaution to prevent sand, silt, and clay particles from clogging the resin bed. Also, the system should be designed to backwash with non-contaminated water.

Know the maintenance requirements of an ion exchange system and make sure maintenance takes place at recommended intervals or when conditions indicate.

For more information on treatment, contact two organizations that certify home drinking water treatment systems: the National Sanitation Foundation (NSF) at and the Water Quality Association at