Though Philadelphia tap water meets federal standards for safe drinking, it exceeds guidelines set by the nonprofit Environmental Working Group for five chemical contaminants including hexavalent chromium and chloroform, according to the group’s updated tap water database released Wednesday.

Philadelphia is far from alone in exceeding stringent guidelines that the organization says are based on the latest science. The group says it goes beyond federal rules and reviews scientific evidence, legal standards, state guidelines, and health advisories to define its own standards, which are much stricter.

EWG describes itself as nonpartisan. The group’s “dirty dozen” list of produce containing heavy pesticide residue has garnered attention, if not agricultural industry pushback, for years. Its water database has also grown in popularity and is now updated with data from tests conducted in 2016 and 2017.

“Most Americans assume the federal government ensures their tap water is safe to drink,” EWG president Ken Cook said in a statement. “Our Tap Water Database shines a light on an ugly reality: The Safe Drinking Water Act is broken, and the water millions of Americans drink is contaminated with unhealthy pollutants like PFAS, pesticides, arsenic, hexavalent chromium and more.”

The group sets limits based on the amount estimated to cause no more than one cancer case per million people who drink the water over a lifetime.

Alexis Temkin, an EWG scientist with a Ph.D. in endocrine disruption, said the greatest threats could come not from a single chemical found in a utility’s drinking water, but from all of them combined — even if levels of individual compounds don’t exceed guidelines.

“For some of these contaminants, it might be helpful to look at them all together,” Temkin said.

In a statement, the Philadelphia Water Department said it “is committed to protecting public health and meets or surpasses all state and federal health standards for tap water. PWD complies with all requirements of the Environmental Protection Agency and the Pennsylvania Department of Environmental Protection for drinking water that are designed to protect public health.”

The department says that it “continuously and proactively” monitors drinking-water quality and that its latest reports are publicly available.

In Philadelphia, Temkin said, most chemical compounds that exceeded EWG guidelines are likely the byproduct of disinfecting the water.

The Water Department has to comply with National Primary Drinking Water Regulations for more than 90 contaminants. It also has to follow secondary standards for 15 contaminants that aren’t enforced but that have suggested levels. There is also a separate Lead and Copper Rule. Philadelphia water complied with the latest EPA assessment from the first quarter of 2019.

But Philadelphia exceeded EWG’s guidelines for bromodichloromethane, chloroform, and dibromochloromethane, all part of a group known as trihalomethanes, which are indicative of treating water with chlorine.

Philadelphia’s trihalomethanes registered at 42.9 parts per billion. The legal limit is 80 parts per billion. However, EWG’s guidelines call for no more than 0.15 parts per billion.

Temkin said trihalomethanes are typical byproducts of utilities that draw from waterways and have to disinfect the water to kill off microbes that make humans sick. Chlorine and other disinfectants react with plant and animal waste in water sources to form byproducts that are also contaminants.

Philadelphia draws its water for treatment from the Delaware and Schuylkill rivers. Philadelphia’s three plants treat 230 million gallons of water a day in an elaborate process that screens out solids, doses it with chlorine, and filters through layers of sand, gravel, and carbon. It is dosed again with chlorine to preserve the water on its journey through miles of pipe to individual homes.

The chlorination affects the taste of Philadelphia water.

The city also exceeded EWG guidelines for hexavalent chromium and nitrates.

Temkin said the chromium likely comes from industrial sources, while nitrates are typically associated with farming.

There are no federal standards for the family of compounds known as PFAS that are causing national concern, but there has been initial federal reporting. Philadelphia has launched its own pilot testing program for PFAS.

EWG notes that the EPA has not set a new tap-water standard for nearly 20 years and that some standards are decades older than that. So it recommends that people use activated carbon, reverse osmosis, or ion exchange filters depending on the chemicals found in their drinking-water supply listed in the database, which is searchable by zip code.

EWG’s database was first published in 2005 to collect data from water utilities’ reports to the EPA and state agencies. EWG says it analyzed 32 million test results for 517 different contaminants or contaminant groups.