Excellent Water Quality
Water Quality Summary
Tap water quality in Mercer Island, Washington (98040) receives an overall grade of A (Excellent) with a score of 93 out of 100, based on analysis of EPA compliance data, contaminant testing, and violation history. This is 18 points above the Washington state average of 76. Compared to the national average (75), this area performs significantly better. The area is served by 2 water systems providing water to approximately 30,785 people, using surface water and groundwater sources. Testing has found elevated levels of Lead that warrant attention. The area has a clean violation record over the past 5 years — a positive indicator of consistent water quality management.
A score of 93/100 means the water supply in Mercer Island, WA meets or exceeds all EPA standards with minimal issues. Contaminant levels are well within safe limits, and the water system has maintained a strong compliance record. While no water supply is guaranteed perfect at the tap due to household plumbing, this is among the best-scoring areas in the country.
Health Information
Lead is a toxic metal that can leach from aging pipes and plumbing fixtures.
Even low levels of lead exposure can cause developmental delays in children, kidney damage, and cardiovascular effects in adults. The EPA action level is 15 ppb, but health experts recommend no safe level of lead in drinking water.
Lead enters water primarily through corrosion of lead service lines, lead solder, and brass fixtures — especially in homes built before 1986.
If lead is detected above 1 ppb, consider using a certified lead-removal filter (NSF/ANSI 53) for drinking and cooking water. Run cold water for 30 seconds before use if water has been sitting in pipes.
Common Questions
Based on EPA data, tap water in Mercer Island, Washington receives a grade of A (Excellent) with a score of 93/100. This indicates the water meets federal standards and has relatively few concerns. However, individual homes may still have localized issues such as lead from old plumbing.
ZIP code 98040 is served by 2 water systems using surface water, groundwater sources, providing water to approximately 30,785 people. Multiple source types mean your water may come from a blend of surface and underground sources.
Lead was detected at 6.3 ppb in Mercer Island, Washington. While this is below the EPA action level of 15 ppb, it exceeds the health guideline of 1 ppb recommended by health organizations. Consider a certified lead filter, especially if you have young children.
No PFAS ("forever chemicals") were detected in water systems serving Mercer Island, Washington during the most recent EPA monitoring period (UCMR5). However, not all water systems have been tested for all PFAS compounds, and new contamination can occur over time.
Water systems serving Mercer Island, Washington have zero violations in the last 5 years. This is a positive indicator of consistent regulatory compliance and water quality management.
Based on detected contaminants (lead), residents in Mercer Island, Washington should consider: NSF/ANSI 53 certified filter — specifically rated for lead reduction. Pitcher filters (like Brita Longlast or PUR) and under-sink systems both work. Always look for filters with NSF/ANSI certification for the specific contaminants you want to remove.