6.2 Water Treatment Challenges
Selecting a water treatment system can be a complex decision requiring knowledge of water chemistry and treatment methods. There is no single treatment technology that treats all contaminants. Treatment systems must be chosen based on the unique water chemistry of each well and must consider which contaminants must be reduced to meet water quality targets, as well as pre-treatment requirements for the selected technology to work properly.
Many domestic well owners do not have the knowledge needed to choose and install their own treatment systems and, therefore, they often rely on well owner educational websites and water treatment companies for help. The water treatment industry is not regulated in most jurisdictions, although there are professional associations that offer voluntary certification to promote high professional standards within the industry. The lack of regulation of the water treatment industry leaves well owners potentially vulnerable to poor advice. A study in Pennsylvania, USA, found that 10 percent of well owners had been sold treatment equipment they did not need, and other surveys have reported that obtaining impartial advice on water treatment equipment is a common problem (Chappells et al., 2014).
Once an appropriate water treatment system is selected and installed, it requires regular monitoring and maintenance to ensure the treatment is effective and the water is safe to drink (Figure 14). As discussed previously, most well owners do not monitor their water quality regularly and, therefore, they are vulnerable to contaminant exposure if their treatment system fails. Surveys of household arsenic treatment systems show that it is common for treatment systems to fail. One study that tested raw and treated water in domestic wells in several states in the United States reported that approximately 23 percent of arsenic treatment systems were not in compliance with arsenic drinking water guidelines (Zheng, 2017).
Figure 14 – Steps needed to ensure that well water is safe to drink, including initial testing to identify contamination, installation of an appropriate treatment system, followed by maintenance and monitoring of the treatment system (modified from Zheng and Flanagan, 2017).
As an example of the challenges of selecting and maintaining a water treatment system, consider an ultraviolet light, which is one of the most commonly used methods for treating microbial contaminants in domestic well water. These systems are simple to operate because they use an ultraviolet light to deactivate microbial contaminants as they flow past the light. In the selection of an ultraviolet treatment system, however, the well owner must consider the intensity of the ultraviolet light (different intensities are needed for different concentrations and types of pathogens), the water flow rate (which controls the water’s contact time with the light and thus its effectiveness), and the pre-treatment requirements to remove turbidity, color (which reduce light penetration), and dissolved solids (which may precipitate on the light’s protective glass sleeve and reduce light intensity). Pre-treatment methods include sediment filters to remove turbidity, and water softeners to remove hardness, iron, and manganese. Once an ultraviolet system is installed, it must be maintained by replacing the light bulb annually and regularly cleaning the protective glass sleeve that houses the ultraviolet light bulb. If well owners are unlikely to carry out regular water quality monitoring, they may also be unlikely to carry out regular treatment system maintenance.
An ultraviolet system for treating microbial contaminants is a relatively simple system compared to others, such as an arsenic treatment system. For arsenic in domestic well water, there are multiple treatment technologies to choose from (e.g., reverse osmosis, adsorption media, anion exchange) and not all technologies are effective for all types of arsenic. Dissolved arsenic can be present as Arsenic (III) and Arsenic (V), depending on redox conditions, which can change over time (e.g., due to seasonal variations) and/or with pumping. Well owners will typically not know which type of arsenic is present in their well water because arsenic speciation is not included in a standard domestic well water quality analysis. One of the most common household treatment methods for arsenic is reverse osmosis and this method is known to be poor at removing Arsenic (III). To compensate for this, a pre-treatment unit can be added that oxidizes Arsenic (III) to Arsenic (V), which is more effectively removed by reverse osmosis. Given the complexities of water treatment, it is understandable that many homeowners rely on a water treatment company to choose and install a treatment system. This may result in the well owner not understanding what type of treatment system they have or even what it is designed to treat. One study that surveyed 99 owners of domestic wells in Maine, USA, found that 26 percent had mistakenly thought their sediment filter or water softener was for arsenic treatment (Zheng, 2017).