Arsenic is an element that seeps into groundwater through the natural weathering of rocks and minerals. It is odorless, tasteless, and invisible in water, making its presence undetectable without specialized testing. Long-term consumption of water containing inorganic arsenic poses serious health risks, including an increased probability of various cancers and cardiovascular issues. Private well owners are responsible for the safety of their water supply, making effective removal methods necessary to safeguard health.
Testing Your Water and Pretreatment Requirements
The first step in addressing water contamination is to have a professional laboratory perform a certified water test. Arsenic levels can vary significantly between nearby wells, and the results are necessary for selecting the correct treatment technology. The United States Environmental Protection Agency (EPA) has established a Maximum Contaminant Level (MCL) for arsenic at 10 parts per billion (ppb), and any concentration above this requires remediation.
Testing must also include an arsenic speciation analysis, which determines the ratio of the two inorganic forms: Arsenic III (arsenite) and Arsenic V (arsenate). Arsenic V is the charged form and is relatively simple to remove using common treatment methods. Arsenic III is uncharged at typical water pH levels, making it significantly more difficult for most filtration systems to capture.
If Arsenic III is present, a pretreatment step is mandatory before filtration can be successful. This process, called oxidation, converts the harder-to-remove Arsenic III into the more reactive Arsenic V. Common oxidizing agents used for this conversion include chlorine, hydrogen peroxide, or potassium permanganate, which must be injected into the water upstream of the main filter.
Point-of-Use Filtration Systems
Point-of-Use (POU) systems are installed at a single tap, such as the kitchen sink, and are designed to treat only the water used for drinking and cooking. These localized systems are generally the most common and cost-effective approach for households with moderate contamination levels. POU systems utilize two primary technologies to reduce arsenic concentrations to below the 10 ppb standard.
Reverse Osmosis (RO) is a highly effective POU method, which forces water under pressure through a semi-permeable membrane. This membrane blocks larger molecules, including charged contaminants like Arsenic V, while allowing purified water molecules to pass through. A typical RO unit is a multi-stage system that includes pre-filters. These pre-filters protect the membrane from sediment and chlorine, ensuring the longevity and efficiency of the arsenic removal process.
Adsorption filters are another effective POU option, utilizing specialized media that chemically bind to the arsenic molecules. These filters often contain media such as Activated Alumina or iron-based sorbents, which have a strong affinity for Arsenic V. The adsorption process captures the contaminant within the filter cartridge. The cartridge requires regular replacement once the media’s capacity is exhausted.
Whole-House Treatment Technologies
Whole-House, or Point-of-Entry (POE), systems treat all water entering the home. They provide a comprehensive solution necessary for very high contamination levels or when arsenic exposure is a concern for bathing and other uses. These systems are larger, more complex installations that require a dedicated space and professional installation to handle the high flow rates of the entire water supply.
Activated Alumina (AA) employs large tanks filled with granular media. The effectiveness of AA is strongly dependent on the water’s pH level, with optimal arsenic removal occurring at a slightly acidic pH (5.5–6.0). If the household water is naturally alkaline (pH above 8.2), the system may require continuous chemical injection for pH adjustment to maintain adsorption capacity.
Ion Exchange (IE) systems employ a resin bed to remove arsenic. The resin exchanges the charged Arsenic V ions for less harmful ions, such as chloride, as the water passes through the tank. IE systems can be sensitive to high sulfate concentrations in the water, as sulfates compete with arsenic for binding sites on the resin, potentially reducing removal efficiency.
Another POE approach is an Oxidation/Filtration system, which combines the necessary pretreatment step with a specialized filter media. These systems often use an oxidizing agent, like a low dose of chlorine, followed by a filter material such as manganese dioxide or greensand. This captures the newly converted Arsenic V. This combined method is effective for well water that contains both Arsenic III and high levels of iron, as the oxidation process precipitates the iron, which aids in the arsenic removal.
Long-Term Maintenance and System Selection
Selecting the appropriate arsenic removal system requires careful evaluation of the initial water test results and the household’s water usage goals. A POU system is sufficient if arsenic levels are low to moderate and the primary concern is only for drinking and cooking water. A POE system is a more robust solution for high arsenic concentrations or for homes that require treated water at every faucet and appliance.
Ongoing maintenance is necessary to ensure continuous performance. All systems require regular performance testing of the treated water to confirm that arsenic levels remain below the 10 ppb limit. For adsorption and RO systems, the filters or membranes must be replaced according to the manufacturer’s schedule, based on the incoming arsenic concentration and water volume.
Ion exchange and Activated Alumina systems require periodic chemical regeneration or a complete replacement of the media, which represents a significant long-term operational cost. Spent media from large POE systems will contain concentrated arsenic and may be classified as hazardous waste, requiring specialized disposal according to local environmental regulations. To ensure a system is both safe and effective, always select a unit certified by a recognized third party, such as those meeting NSF/ANSI Standard 53 or NSF/ANSI Standard 58 for reverse osmosis systems.