Treatment Alternatives

Figure 13: Filtration guide

Today, well owners have access to several water treatment systems to help control minerals and contaminants and to disinfect their well water. However, choosing a water treatment system is no easy task. Depending of the volume of water and degree of contamination, the well owner should consider professional assistance in selecting and installing well water treatment systems. The process of selection is often confounded by incomplete or misleading information about water quality, treatment options and costs. The following paragraphs outline the major well water treatment options.  Further details on types, uses, point of use, and costs of these home water treatment systems and are provided in the Arizona Know Your Water companion booklet.

Each of the following water treatment options should be carefully evaluated when considering water treatment alternatives to reduce the levels of mineral (inorganic) and carbon-based (organic) contaminants. These four methods are well proven and widely accepted by experts and regulatory agencies as being efficient for the reduction of contaminants in water. Use the Filter Application Guide (Figure 13) to help determine which system is right for you.

Particle and Microfiltration

Particle filtration is a process that removes small amounts of suspended particles, ranging in size from sand to clay, from water. It can be used alone or prior to other water treatment devices installed in your home system. Home filters are not intended to filter large amounts of particles. However, larger filtration systems (usually located near the well head or at the home point of entry) are available to remove well sediments and particulates, depending on the well water quality. Microfiltration may also be used to remove some bacteria and large pathogens, like cysts (Giardia and Cryptosporidium). Note that microfiltration should not be relied on to disinfect water with high concentrations of bacteria and viruses, instead chemical disinfection should be used. Other forms of filtration include ultrafiltration and reverse osmosis. See Figure 13.

Figure 14: Point of use carbon filter

Activated Carbon Filter

Activated carbon filtration, often used as a point of use treatment, may be selected to reduce unwanted taste, odor, and low concentrations of organic chemicals (such as pesticides and solvents) from drinking water. Activated carbon will also reduce radon gas and residual chlorine. Larger filters are available to treat high volume of water but these usually require professional installation and maintenance. Carbon filters will not remove or reduce major inorganic ions (e.g., sodium, calcium, chloride, nitrate and fluoride or metals). However, some carbon filters can reduce lead, copper and mercury. Activated carbon filters will not soften the water or disinfect it. If the source water is cloudy, a particle filter should be used before the activated carbon filter in order to remove particles that may plug or reduce its efficiency.

Reverse Osmosis

Reverse osmosis (RO) is becoming a common home treatment method to reduce total dissolved solids (TDS) in drinking water. RO, probably best known for its use in water desalinization projects, can also reduce chemicals associated with unwanted color and taste. It also may reduce pollutants like arsenic, lead and many types of organic chemicals.

RO treatment is not effective for the removal of dissolved gases such as radon, or for some pesticides and volatile organic chemicals such as solvents. Consumers should check with the manufacturer to determine which contaminants are targeted and what percent of the contaminant is removed.

RO not is recommended for sediment (particle) and pathogens. Pretreatments such as particle filtration (to remove sediments), carbon filtration (to remove volatile organic chemicals), chlorination (to disinfect and prevent microbial growth), pH adjustment or even water softening (to prevent excessive fouling produced by water with excessive hardness) may be necessary for optimum RO functioning.

Distillation

Distillation effectively removes inorganic contaminants (suspended matter including minerals and metals) from water. Since distilled water has no minerals, some people claim distilled water tastes flat or slightly sweet. Distillation kills or removes microorganisms, including most pathogens. Distillation can also remove organic contaminants, but its efficiency depends on the chemical characteristics of the contaminant. Volatile organic chemicals (VOCs) like benzene and TCE vaporize along with the water and re-contaminate the distilled water if not removed prior to distillation. Some distillation units may initially purge some steam and volatile chemicals. These units should be properly vented to prevent indoor air contamination. Some home distillation units have activated carbon filters to remove VOCs during distillation.

Ion Exchange—Water Softening

Ion exchange units that replace calcium and magnesium ions from water are known as water softeners. They may also remove varying amounts of other inorganic pollutants such as metals, but they will not remove organic chemicals, pathogens, particles, or radon gas. Water softener units work most efficiently with particulate-free water.  Note that soft water, in particular with elevated sodium levels, should not be used to water house plants, garden vegetables or yard plants with low salinity tolerance.  Soft water may not be suitable for drinking due to its salty taste and elevated levels of sodium or potassium.

Pathogens-Disinfection

Waterborne contaminants must be either filtered out of the water or killed (inactivated) to make the water safe to drink.  The methods discussed above are not suitable (except for distillation) for this purpose. As a rule water must be disinfected using chemicals (oxidizing agents such sodium or calcium hypochlorite, chloramines, chlorine and ozone) or UV radiation. Water disinfection will not remove inorganic contaminants from water but it may change the chemical species of some of them and is likely to form disinfection byproducts that may be of concern.  Chlorination guidelines for domestic wells are also discussed below.  See also the Arizona Know your Water booklet for a more detailed discussion on water chemical and UV-radiation disinfection methods and guidelines.

Equipment for Continuous Chlorination of Domestic Wells

Continuous chlorination of a domestic water supply can be done by various methods: chlorine pump, suction device, aspirator, solid feed unit, and batch disinfection. The injection device should operate only when water is being pumped, and the water pump should shut off if the chlorinator fails or if the chlorine supply is depleted. Consult with a professional for equipment selection and tank requirements. For example, in a domestic well system, the minimum-size holding tank is determined by multiplying the capacity of the pump by a factor of 10. Thus, a 5 gallon-per-minute (gpm) pump requires a 50 gallon holding tank. Other methods to control contact time include the use of pressure tanks and coils.

Boiling

Two minutes of vigorous boiling ensures biological safety.  Boiling kills all organisms in water (whereas chlorination reduces them to safe levels).  But boiling is costly and practical only as an emergency measure.  Remember that once boiled, cooled water must be protected from re-contamination.

Emergency Disinfection

The use of household chemicals (such as bleach or iodine) to disinfect water without the appropriate equipment or technical supervision should only be considered under emergency situations. For a list of these chemicals and their safe use, see the EPA website: www.epa.gov/OGWDW/faq/emerg.html.