Arlington Heights receives its municipal drinking water from Lake Michigan. The Village transitioned from deep-well groundwater to Lake Michigan surface water beginning in 1985. The City of Evanston treats the Lake Michigan water, and the Northwest Water Commission receives the treated water and distributes it to Arlington Heights. The Village maintains six deep wells for emergency purposes; according to the 2025 report, no emergency well water was distributed during 2025.

At Evanston's treatment plant, the reported treatment processes include flocculation, sedimentation, rapid sand filtration, and disinfection. Evanston also adds fluoride and chlorine and uses polyorthophosphate as a corrosion inhibitor. Arlington Heights monitors the disinfectant residual and can add chlorine when necessary to maintain the required residual within its distribution system.

The Village's current water-quality webpage likewise states that Evanston provides complete treatment and filtration and that the Northwest Water Commission distributes the treated water to Arlington Heights. (Vah)

The Village's 2025 Water Quality Report, reported in June 2026, states that Arlington Heights drinking water met applicable federal and state drinking-water standards during 2025 and that the system did not exceed state or federal contaminant levels or other water-quality standards.

The 2025 Arlington Heights lead and copper data reported a lead 90th percentile of 8.83 ppb, below the 15 ppb action level. One sampling site was above the action level, but the table reports no lead violation. Copper had a 90th percentile result of 0.138 ppm, below its 1.3 ppm action level, with no sites above the action level and no violation.

The report does document a Consumer Confidence Rule adequacy/availability/content violation associated with the previous annual report. The Village explains that a required lead informational statement had been omitted and some content was incorrect. As corrective action, the 2025 report includes the required corrected information, and the Village says it implemented a CCR review checklist and management-review process. This was a reporting-content violation, not a finding that the distributed drinking water exceeded a contaminant standard.

The report also lists elevated radionuclide measurements from samples of the Village's emergency backup wells. Those results should not be confused with water distributed to customers: the report separately states that no emergency well water was distributed during 2025, and the tables mark these results as having no violation.

Arlington Heights' report specifically addresses periodic taste and odor conditions. It says objectionable tastes or odors may occasionally result from changes involving chlorine or algae in Lake Michigan. Algae interacting with chlorine can create an earthy or musty taste and odor, while chlorine-related conditions can also produce a noticeable chlorine odor. The report states that Evanston has implemented enhanced treatment techniques to help mitigate these occurrences.

The report also describes turbidity as a measurement of water cloudiness and reports a highest single measurement of 0.15 NTU, with no turbidity violation and 100% compliance with the reported monthly treatment limit.

The Illinois EPA source-water assessment cited in the report considers surface-water sources susceptible to potential pollution because contaminants can migrate toward surface-water intakes. For Evanston's Lake Michigan source, the report notes potential influences including the North Shore Channel, wet-weather flows, and proximity to a major shipping lane. It also states that Evanston's intakes are far enough offshore that shoreline impacts are not considered a water-quality factor and describes Evanston's treatment as highly protective.

Lead can enter drinking water through service lines and household plumbing. Arlington Heights has developed a water-service-line material inventory, and the Village's current lead-information page states that residents can check whether a property has a known lead service line. The Village also notes that lead action levels are evaluated using the 90th-percentile tap result and that an individual sample above 15 ppb does not by itself constitute a regulatory violation. (Vah)

The 2025 report also contains PFAS monitoring results. It reports PFOA at a highest detected level of 2.3 ppt and PFOS at 2.0 ppt, with no violation recorded in the report. PFOA was above the report's listed Illinois EPA guidance level of 2.0 ppt but below the 4.0 ppt federal level shown in the table. U.S. EPA's current PFAS rule establishes a federal MCL of 4.0 ppt for both PFOA and PFOS, with public water systems required to complete initial monitoring by 2027 and implement necessary compliance solutions by 2029. (US EPA)

As the municipal report explains, some people—including certain immunocompromised individuals, older adults, and infants—may be more vulnerable to contaminants or infections and should obtain individualized drinking-water advice from their healthcare providers when appropriate.