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Glass of water

Water well treatment systems are generally either point-of-use systems or whole-house systems. Some treatment options require more than one method (or a treatment chain) to address the water quality issue.


Filtration treatments utilize porous materials to remove suspended particles.

One way to visualize this is by thinking of a coffee filter. Each morning, when you pour coffee grounds over your filter, you hope that no large particles make their way into the cup. The smaller the filter pores, the smaller the particles it can catch and prevent from entering the drink. The size of the pores in the filter determines what contaminants will be removed, with smaller pores being able to remove smaller contaminants. For example, a filter with pore sizes of 1 micron or less will trap contaminants larger than 1 micron.

This knowledge is used to design filters that can remove specific contaminants. Filtration processes include particle filtration, microfiltration, ultrafiltration, and reverse osmosis.

  • Particle filtration utilizes materials like sand and fibers to remove sediment particles, generally sized about 0.002 mm to 2mm. It can also treat acidic water if preceded by the addition of soda ash or remove dissolved iron or manganese when preceded by continuous chlorination, ozonation, or aeration.
  • Microfiltration systems have microscopic pores that can remove microorganisms like Giardia and Cryptosporidium.
  • Ultrafiltration is a more aggressive form of microfiltration and is used in industrial water treatment processes to remove viruses and dissolved organic molecules.

Some filters can even contain reactive materials to remove specific contaminants. For example, iron or activated carbon can be added in a filter to remove arsenic and organic chemicals, respectively.

Filtration systems should be used as instructed. A filter made to remove one contaminant should not be used to attempt removing a different contaminant, such as using a bacteria filter to remove sediment. Filters and other treatment systems should come with maintenance instructions from the manufacturer. Contaminants build up in the filtration media as it treats the water, so manufacturer recommendations for replacement or backflushing should be followed. Backflushing refers to the regular maintenance practice of reversing the water flow through the filter to flush out any debris that might be blocking the filter’s pores. Only certain filtration systems utilize backflushing, and it should not be performed unless the manufacturer recommends it.

As with all treatment systems, filtration is not always the answer. High concentrations of bacteria or viruses should be addressed by chemical disinfection or distillation.

Activated Carbon Filters

Activated carbon filtration is a form of ultrafiltration that incorporates carbon-rich materials like coal or charcoal in the filtration media to bind with and remove certain chemicals. In addition to its reactivity, the carbon has been processed to increase its porosity. These filters are common for taps and water pitchers.

Again, recommendations for product use should be followed. It is recommended that professionals install and maintain whole-house systems. When well water is cloudy, the activated carbon filter is at risk of clogging and reduced efficiency. A particle filter should be installed to treat the water before it reaches the activated carbon. Replacing filters is important to avoid the growth of microorganisms and clogging.

Activated carbon filters are capable of removing low concentrations of organic chemicals (e.g., pesticides and solvents), copper, lead, mercury, and radon gas. They are not known to remove inorganic ions (e.g., calcium, chloride, fluoride, nitrate, and sodium). For aesthetic purposes, activated carbon filters can remove bad tastes and odors but will not remove hardness.

Reverse Osmosis

In reverse osmosis systems, pressure forces the untreated water (which has a higher solute concentration) through a membrane and into an area of lower solute concentration. A solute is a substance that can be dissolved in another substance. For example, sugar is a solute that dissolves in water. Osmosis moves water from an area of lower solute concentration to an area of higher solute concentration. The targeted contaminants are left behind, meaning some treated water gets produced, but a waste product also forms.

Like activated carbon filters, reverse osmosis filters are common in point-of-use systems. The water requirement and creation of a waste product makes reverse osmosis impractical for whole-house systems. The treatment process requires a larger amount of water than the treated water that is created. If four gallons enter the system, approximately one gallon of treated water will be produced. Additionally, the waste brine created contains elevated amounts of the contaminants removed from the treated water, such as total dissolved solids (TDS), which can cause elevated salinity. The contaminants could negatively affect septic systems and surrounding soils if produced in large amounts.

Reverse osmosis is successful at removal of TDS, so it is frequently used to desalinate water. It can also remove contaminants that cause odor and bad tastes, arsenic, uranium, and some organic chemicals. It is not effective for the removal of dissolved gases (e.g., radon), some pesticides, volatile organic compounds (e.g., degreasers and solvents), pathogens, or sediments.


Distillation removes contaminants by boiling water, collecting the steam, and condensing it back into water. The resulting water is nearly purified, as the contaminants are left behind when the steam rises. Distillation systems are capable of removing inorganic contaminants (i.e., minerals and dissolved metals), microorganisms, many pathogens, and some organic matter. Because the minerals are removed, distilled water is usually tasteless.

The presence of volatile organic chemicals (VOCs) can cause problems in distillation systems, but these can be addressed. VOCs are able to vaporize during boiling and travel with the steam, so VOCs should be removed with another form of treatment prior to distillation or the distillation unit should contain an activated carbon filter. Additionally, some units require proper venting so steam and VOCs that purge from the unit do not cause air contamination inside.

There are many considerations for the use of distillation units. Distillers are typically point-of-use systems used only for drinking water because of the amount of time required to treat water, the amount of water the system requires, and the need for a power source. A typical home unit can produce one gallon of treated water in roughly four hours, meaning about six gallons could be produced in one day. The treated water is typically kept in a storage tank until it is used. The water-use efficiency of a distillation unit generally depends on the type of condensing system. Air-cooled units use less water and create about one gallon of untreated water for every gallon of water that is treated. Water-cooled units require much greater amounts of water and may need as much as 15 gallons to produce one gallon of treated water. A power source, typically electricity, is required to boil the water. Higher producing units will require more electricity. The electrical costs for treatment of one gallon of water is approximately 25¢-35¢.

Manufacturers should have recommendations for cleaning the unit or replacing parts. Cleaning frequency and materials can vary based on the constituents and their concentration in the incoming water.

Distillation removes sediment, salt, total dissolved solids, fluoride, nitrate, heavy metals (lead, copper, etc.), arsenic, and bacteria.


Aeration systems work by introducing oxygen into the water via an aerator. This process oxidizes contaminants, causing them to form solids which can be filtered out of the water. Aeration may remove substances like dissolved iron, manganese, and radon. With an aeration system, regular backwashing of the filter is required, and care should be taken to avoid filter obstruction.

Aeration removes dissolved iron or manganese, and radon.


In contrast, deaeration systems mixes air with water to remove dissolved gases from the water. This method may remove substances like dissolved hydrogen sulfide gas and radon.

Deaeration removes dissolved hydrogen sulfide gas, and radon.

Ion Exchange

Ion exchange systems are designed to remove either cations (positively charged particles) or anions (negatively charged particles) from water and exchange them for less objectionable ones. This requires the use of an exchange material loaded up with certain ions. Mixed media units also exist to exchange both cations and anions.

Caton Exchange

Cation exchange units are primarily used to soften hard water. Typically, the exchange media is loaded with sodium (some newer and more expensive units may use potassium) and exchanges the sodium for calcium and magnesium in the water. Barium, radium, iron, and manganese may also be removed this way.

Water softeners can be used as whole-house systems but are not usually needed for drinking water or outdoor use. Because the cations are typically replaced with sodium, softened water may taste salty and is not ideal for watering salt-intolerant plants. Point of-use softeners are helpful for hot water use, bathing, and laundering to prevent scale formation or detergent residue.

As water softeners are used, the exchange sites (where the sodium is located) are replaced by ions from the water and become unavailable for exchange. Therefore, maintenance includes a process called regeneration, where a brine is passed through the media to release the ions and replace them with sodium. This may be done manually, semi-automatically, or automatically, so it is important to read manufacturer instructions. The media will also decrease in effectiveness over time and need replacement. Iron and sediments can cause serious problems in water softeners, so pretreatment may be beneficial.

Cation exchange removes hard water (calcium and magnesium), dissolved iron, manganese, can also treat cadmium, copper, and zinc.

Anion Exchange

Anion exchange systems usually have media loaded with chloride or hydroxide ions to remove sulfate, nitrate, and arsenic. Point-of-use systems are typically enough and only needed for drinking and cooking water.

Because anion exchange removes contaminants harmful to human health, the systems should be monitored to ensure proper removal. Like cation exchange units, anion exchange units require regeneration as part of maintenance. However, because the waste brine contains substances like arsenic, it requires more careful disposal. Make sure to follow the safety precautions recommended by the manufacturer. Pretreatment may help avoid problems with iron and sediments. Post-treatment may also be needed, as anion exchange tends to lower the water pH.


Water containing pathogens can be a serious threat to the consumer, so bacteria should be killed and viruses should be inactivated before consumption. Of the discussed methods so far, only distillation is appropriate for continuous pathogen removal. Disinfection is another suitable process and typically involves exposure to ultraviolet (UV) radiation or the addition of chlorine or ozone.


Chlorination is the addition of chlorine to water to kill pathogens. It comes in dry forms as calcium hypochlorite, Ca(ClO)2, and in liquid form as sodium hypochlorite, NaClO. The effectiveness of chlorination depends on many factors. In addition to the chlorine concentration, the amount of time the chlorine is in contact with the water, known as contact time, is important. Water quality of the untreated water can affect chlorination, as some contaminants (i.e., iron, manganese, hydrogen sulfide, ammonia, and organic materials) can combine with chlorine and make it unavailable for the targeted contaminants. This can be addressed by pretreatment or the addition of extra chlorine. Water temperature and pH can affect chlorination, and ideal conditions are considered high temperature with low pH.

The amount of chlorine needed varies by chlorination method.

  • Batch disinfection uses enough chlorine to treat large batches, which are then stored for later use.
  • Simple chlorination maintains a low concentration of chlorine to disinfect water as it is needed.
  • Super chlorination uses a much larger concentration of chlorine to treat water quickly and usually requires dechlorination by an activated carbon filter following treatment.
  • Shock chlorination. New wells, newly repaired wells, wells with bacterial contamination, and temporarily contaminated wells are often treated by shock chlorination. During shock chlorination, household liquid bleach is circulated through the well and plumbing system. See Flooded Wells: Shock Chlorination to learn more about the shock chlorination process.

Be sure to follow manufacturer instructions for maintenance. This may include checking and lubricating parts, cleaning, and refilling chlorine. Maintenance should be performed with all power chords unplugged. Follow recommendations for handling chlorine, as it can be a skin irritant and is potentially poisonous if swallowed.

Ultraviolet Radiation (UV)

UV radiation kills common pathogens by emitting light from a bulb at a specific wavelength. Unlike chlorination, UV radiation treatment can be fast without adding anything to the water or causing additional taste or odor.

In addition to the intensity of the UV light and contact time, the success of UV radiation is affected by water depth and quality. Light penetration reaches down to a depth of about three inches, so the water must be supplied in a manner that allows contact throughout the supply. Because the pathogens need to be exposed to the UV light, suspended particles in the water can interfere with treatment. Therefore, UV treatment is often paired with a filtration method and should be the last treatment used in a sequence. Manufacturers should provide information on cleaning the system and replacing bulbs. Cleaning is important to ensure dirty fixtures don’t block UV light entry into the water.


Ozone is a highly reactive gas commonly used in water treatment. Ozonation is a point-of-entry treatment where ozone is added to the water to kill pathogens and oxidize contaminants like iron and manganese, causing them to form solids that can be filtered out of the water. Because ozone is unstable, it does not last long in water and will not remain.

Ozonation removes bacteria, viruses, and can also remove dissolved iron and manganese when combined with sediment filtration.

Emergency Disinfection

Storing a package of bottled water provides an easy back-up supply of drinkable water in case of emergencies. However, there are other options if bottled water is not available. Water can be boiled for two minutes to kill pathogens, but this concentrates other constituents like salts and minerals in the water, so it is not recommended for everyday use. The EPA has in depth instructions for use of bleach or iodine in dire situations when boiling water isn’t possible.

Do not use bleach that is scented, color safe, contains additional cleaners, or has been stored for longer than a year. Add bleach to water with a dropper, stir, and let sit for 30 minutes. The water will have a slight chlorine odor. Sanitizing household bleach typically contains 6 or 8.25 percent sodium hypochlorite. See the table below for the amounts of bleach to add.


Bleach Amounts for Emergency Disinfection

Water VolumeAmount of 6% Bleach to AddAmount of 8.25% Bleach to Add
1 quart or liter2 drops2 drops
1 gallon8 drops6 drops
2 gallons16 drops (1/4 tsp.)12 drops (1/8 tsp.)
4 gallons1/3 tsp. 1/4 tsp.
8 gallons2/3 tsp.1/2 tsp.


After Treatment

After treating your well system, perform regular testing maintenance to keep the system up to its highest quality. Replace the water filter when required and be informed of the requirements for each piece of treatment equipment that you own.