Seattle tap water: soft 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 1.5 gpg, Seattle water is soft, the 3rd-softest of the 34 systems we track. Scale won’t be a problem.

What to do: Skip the softener. It would cost money and salt for no benefit.

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 testing found no PFOA or PFOS in Seattle’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: Seattle uses free chlorine. It’s the one that can give tap water a slight pool smell, and it’s easy to filter.

What to do: For taste, any carbon filter certified to NSF/ANSI 42 for chlorine works.

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 →

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: Seattle’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.