Last week an environmental advocacy organization called the Environmental Working Group (EWG), released an update to its “National Drinking Water Database”. The database contains self-reported data collected by 49,000 public water utilities in all 50 U.S. states over five years, 2010 - 2015.

EWG extracted its data from two sources. The first source was state compliance databases, which is data water systems provide to their states to meet ongoing regulatory requirements. Data on unregulated contaminants collected by water systems and sent directly to the U.S. Environmental Protection Agency (EPA) was also used. The EPA data was collected under the Unregulated Contaminant Monitoring Rule (UCMR), a rule under the Safe Drinking Water Act that requires EPA to issue a new of list unregulated contaminants every five years water utilities must monitor for.

We looked over EWG’s database, and more importantly, the report they issued along with it, and found some areas that are misleading. EWG’s analysis compares observed concentrations against maximum contaminant level goals (MCLGs) and California’s public health goals (PHGs) instead of comparing them to existing maximum contaminant levels (MCLs).

There’s a big difference between MCLGs and MCLs: MCLGs are levels of contaminants below which there is no evidence of a potential health risk – this level can be much lower than concentrations where we know harm is occurring. MCLGs are set conservatively, and that is the right thing do to because they are goals. The same is true of PHGs in California. Just like EPA, California is very careful to communicate that it may not be feasible to set the drinking water standard for a contaminant at the same level as the PHG. MCLs are protective standards that water systems must meet, and MCLs are set as close to MCLGs as possible.

Additionally, by looking at UCMR3 data, EWG specifically looked at contaminants that aren’t currently regulated. This means that while water utilities are required to test for and report on the contaminants, EPA has not set a legal limit. While EPA has not set a legal limit on those contaminants, EWG is holding water systems accountable for their presence anyway and has taken the additional step of proposing their own standard.

To protect consumers, EWG recommends the use of home treatment devices to filter tap water. It’s a personal choice whether you filter your water or not, but make sure you make a well-informed decision if you do. Use NSF International as a guide to review independently certified filters, which is what you should aim for. If you choose to buy one, make sure you maintain it, so that it will be effective and not present a source of risk for you and your family.

Be assured that nearly all water utilities in the United States meet EPA’s standards for safe drinking water. But as consumers, it’s our responsibility to make sure we understand our local tap water quality. Review your annual consumer confidence report, and if you haven’t received it already for the year, contact your local water utility. Contact them if you have any questions or concerns about it too. It’s on each of us to understand our tap water because, after all, we rely on it so much every day.