Denver tap water: moderately hard water, no PFOA or PFOS found

Hardness is dissolved calcium and magnesium, picked up as water runs through rock. It isn’t a health issue (EPA has no limit for it). It’s what leaves white crust on faucets, spots on glasses and scale inside your water heater. It’s measured in grains per gallon (gpg); 1 gpg is about 17 mg of minerals in a liter.

Here: At 6.1 gpg, Denver water is in the middle of the scale, the 13th-softest of the 34 systems we track. Some homes notice spots; many don’t.

What to do: A softener is optional. If spots bother you, a small one does the job.

What the research says: Studies tie hard water to more soap use and scale. Observational studies link it with somewhat more eczema in babies, but in the largest trial a softener didn’t improve existing eczema. The studies →

PFAS are a family of thousands of manufactured chemicals used in many consumer and industrial products. They break down very slowly, which is why people call them "forever chemicals." PFOA and PFOS are the two EPA regulates most tightly. They’re measured in parts per trillion (ppt): 1 ppt is about one drop in 20 Olympic swimming pools.

Here: EPA’s 2023–25 testing found no PFOA or PFOS in Denver’s water at or above 4 ppt, the lowest level labs can reliably measure. 29 of the 40 systems we track can say the same; 11 had a sample over the limit.

What to do: Nothing needed by EPA’s standard. If you want PFAS lower still, the same certified filters apply.

What the research says: EPA and the National Academies link PFOA and PFOS exposure to higher cholesterol, lower vaccine response, lower birth weight and some cancers, mostly over years of drinking the water. The studies →

Utilities add a small amount of chlorine, or chloramine (chlorine combined with a little ammonia), so germs can’t grow in the pipes on the way to your tap. EPA allows up to 4 milligrams per liter (mg/L) of either and says water within its standards can be used for drinking, cooking and bathing.

Here: Denver uses chloramine, like 20 other systems we track. It lasts longer in pipes than chlorine and is harder to filter.

What to do: For taste, use catalytic carbon or a filter certified to NSF/ANSI 42 for chloramine. Fish tanks and home dialysis need it removed completely.

What the research says: Health agencies call these levels acceptable for drinking and bathing; dialysis and fish tanks are the exceptions. Studies haven’t shown shower chlorine harms skin or hair. The studies →

Lithium is a metal that occurs naturally in some rock and groundwater. There’s no legal limit in drinking water. EPA screens results against 10 micrograms per liter (µg/L) while it studies whether a limit is needed.

Here: Denver’s highest sample was 10.8 µg/L. EPA compares results to one significant digit, so that rounds to its 10 µg/L screening level and doesn’t count as above it.

What to do: Nothing to do.

What the research says: Some regional studies link natural lithium with lower suicide rates and the largest individual study found no link. EPA’s screening level is cautious, not a harm threshold. The studies →

A health-based violation means the utility broke a federal drinking water rule tied to health: it went over a limit, or skipped a required treatment step. Missing a paperwork deadline doesn’t count.

Here: Denver’s system had none in the five years through September 2026. That’s normal for a large system: 36 of the 40 we track had none.

What to do: Nothing to do.