The quality of municipal drinking water is a primary concern for residents, especially in established cities with older infrastructure. Detroit’s water supply serves a large metropolitan area, and its safety is determined by rigorous federal and state regulatory standards. This article reviews the Detroit water system, focusing on current safety assessments, purification methods, challenges associated with aging pipes, and official oversight processes.
Current Safety Assessment
Detroit’s drinking water meets or exceeds all quality mandates established by the U.S. Environmental Protection Agency (EPA) and the state of Michigan. These conclusions are drawn from extensive and continuous testing required under the Safe Drinking Water Act. Official data from the most recent annual Water Quality Report confirms the water is safe.
The system remains in compliance with the stringent Michigan Lead and Copper Rule. Recent sampling results showed the 90th percentile of lead concentrations in tested homes was significantly below the federal action level of 15 parts per billion (ppb). This indicates the treated water delivered through the distribution system is not posing a widespread public health concern regarding regulated contaminants.
Water Source and Treatment Process
The water supply originates from the Great Lakes, drawing raw water primarily from the Detroit River and Lake Huron. The system is operated by the Great Lakes Water Authority (GLWA), which processes the water at several advanced treatment facilities.
The purification process begins with screens to remove large debris, followed by pre-treatment with chemicals to manage taste and odor. Next, the water undergoes coagulation and flocculation, where chemicals like alum are added to bind microscopic particles into larger clumps called “floc.” These clumps settle out during the sedimentation phase.
After settling, the water is passed through deep-bed filters, often composed of materials like anthracite coal and sand, to remove any remaining fine particles. The final step is disinfection, which involves using chlorine to neutralize bacteria and viruses; some facilities also employ ozone. A residual amount of chlorine is maintained as the water enters the distribution system to protect its quality as it travels to homes.
Addressing Lead and Aging Infrastructure
While the water leaving the treatment plants contains no detectable lead, the primary risk occurs after the water enters the older distribution system. This is common in established cities where service lines—the pipes connecting the water main to individual homes—may be made of lead.
To mitigate the risk of lead leaching from these pipes, the water authority adds a corrosion inhibitor, typically orthophosphate, during the final treatment step. This compound forms a protective coating on the inside walls of the pipes, preventing the lead from dissolving into the water. In October 2024, the authority increased the dosage of this inhibitor.
The Detroit Water and Sewerage Department (DWSD) maintains an active lead service line replacement program, accelerated with state and federal funding. Since 2018, thousands of lead lines have been replaced, with a current goal of replacing approximately 8,000 lines per year. This proactive work aims to permanently remove the source of lead exposure at the service line level.
Regulatory Oversight and Public Reporting
The safety of the Detroit water system is ensured through a multi-layered regulatory structure involving both federal and state agencies. The EPA sets the national standards for drinking water quality under the Safe Drinking Water Act. The Michigan Department of Environment, Great Lakes, and Energy (EGLE) is responsible for enforcing these standards at the state level, including the Michigan Lead and Copper Rule.
Both GLWA and DWSD must adhere to strict monitoring schedules, requiring testing for a wide range of contaminants, including bacteria, nitrates, and various chemicals, at specified frequencies. The results are made accessible to the public annually through the Consumer Confidence Report (CCR). This report details all regulated contaminants detected, compares them to established limits, and confirms the system’s compliance status.
Residents can find the most current Water Quality Report on the Detroit Water and Sewerage Department’s website.