What the research says
What the research says about your tap water
Water readings are only half the story. Here’s what agency reviews, trials and studies say about what those readings do to people, pets and homes, and how strong each finding is.
Short answer
We read 65 sources: agency reviews from the U.S. Environmental Protection Agency (EPA), the Centers for Disease Control and Prevention (CDC), the National Institutes of Health (NIH) and the World Health Organization (WHO), trials, large cohort studies and engineering tests. 22 carry strong evidence. Most findings about hard water are weaker than softener ads suggest, and the household numbers come mainly from 4 industry-funded tests, which we label.
65 sources, each opened and read November 2026
Hard water and your health
Eczema, hair, heart, kidney stones, sodium from softeners, appliances and pets
PFAS and your health
What EPA, the National Academies and the WHO’s cancer agency found, and why the limit is 4 parts per trillion
Lithium in tap water
Why EPA tests for it, how its screening level was set, and the mental-health studies
Chlorine and chloramine
What agencies say, and what happens with dialysis, fish tanks and skin complaints