The document is called a consumer confidence report, but it can be unsettling because it shows just how much stuff is in our water besides two atoms of hydrogen and one of oxygen.
Thanks to the advance of science, officials can now detect tiny amounts - parts per trillion, even - of all sorts of things.
In 16 dense pages, we learn that the Water Department's instruments have detected coliform bacteria, barium, chromium, cyanide, and the herbicide atrazine.
We are all avid flushers, so traces of pharmaceuticals are showing up, too. Not surprisingly, ones in common use top the list - caffeine, nicotine, and the painkiller acetaminophen.
The good news is that all are well below federal limits.
Charles Haas, a Drexel University professor of environmental engineering, has a comforting analogy: You want a smoke detector that activates long before flames hit the ceiling.
"We want to know what's there," agreed the Water Department's deputy commissioner of operations, Debra McCarty. "So we can be on the cutting edge of working with regulators" and others to determine whether new limits should be set.
Our water mirrors our complex world. Regulations now prohibit adding phosphorus to shampoos and soaps because it survives the sewage-treatment process and contributes to algae blooms in streams. But one of its replacements, an estrogenic compound called nonylphenol, is now being detected in water.
It's one of many "emerging contaminants."
Chlorination, to rid water of pathogens, is regarded as one of the great public health achievements of the 20th century.
But chlorine reacts with organic material in the water - think bits of leaves or algae - and forms chemicals that, in quantity, are linked to higher cancer risk.
Hello, trihalomethanes and haloacetic acids.
Department officials' solution is to mix in ammonia so they can reduce the chlorine.
Philadelphia is much like other water systems that rely on "surface water" - streams and rivers - with added challenges.
In a sense, the department deals with a different river every day, depending on weather and other factors. Actually, two rivers; the city has intakes on the Schuylkill and the Delaware.
And the intakes are pretty much at the "bottom" of the watershed, subject to insults from upstream.
Philadelphia deals with a myriad of them, from a flock of geese that hung out - and defecated - near the Belmont intake, to Berks County farm operations that are potential sources of cryptosporidium bacteria, to a salt influx from road treatments during snowstorms.
Prevention trumps treatment. Philadelphia now has a "source water protection plan" that is the envy of the industry. It encourages upstream improvements and is piloting drug take-back programs to reduce prescription-drug flushing.
Then there's radioactive iodine-131. The initial discovery set off a lengthy probe worthy of a mystery novel. Officials now consider the case solved: Thyroid patients treated with the substance are excreting it.
Given that it has a half-life of eight days, it's gone soon. And amounts remain below a regulatory threshold. But still, it's one of those things department officials would rather not be seeing.
Periodically the department visits homes throughout the city to test for lead, a neurotoxin that isn't in the main pipes, but might be in pipes leading to individual homes.
In this report, they relate finding it in two of the 92 homes tested. The department advises residents to flush the pipes by letting the faucet run for a few minutes in the morning - or at other times when the water hasn't been running for a while.
One substance that there's less of in Philly water is fluoride, which the city has been adding since 1951 to help prevent tooth decay. The city is following new guidelines that recommend a lower amount.
By now, science has advanced enough that we can improve our water just about any way we want, said Nick DeBenedictis, chief executive of Aqua America Inc., which provides water to many Pennsylvania suburbs.
But at what cost? Philadelphians pay half a cent per gallon.
Back in the 1980s, when the city was considering an advanced (as in, expensive) filtration system, DeBenedictis spoke with the late Rep. William H. Gray III, who balked. "Some of my constituents can't afford food," Gray told him.
These days, the department is looking ahead to climate change.
How will they deal with heavy rain? Swollen rivers often carry more sediment and bacteria. Or droughts, which might result in higher concentrations of other contaminants?
GreenSpace: Water Filtration
For extra filtration, here's a guide to methods:
Carbon/charcoal filters: Remove tastes, odors, lead, chlorine, chlorine byproducts (trihalomethanes).
Reverse osmosis: Most systems include carbon pre-filters. They also remove lead, fluoride, arsenic, perchlorates, among others.
Tip: If your filtered water has an odor, it may be time to change the filter!
Adapted from a report by tap water advocacy group, Food & Water Watch.
"GreenSpace," about the environment and health, appears every other week. Contact Sandy Bauers at 215-854-5147, firstname.lastname@example.org, or @sbauers on Twitter. Visit her blog at www.inquirer.com/greenspace.