The evidence library

Everything we read before writing a word about water filters: 201 studies, government reports and datasets, sorted by theme. Each source has its key numbers quoted, its limits stated, an evidence grade and a link. 152 of them are free to read online.

Including the studies that cut against filters. You will find them under health effects, bacteria, minerals and microplastics.
Searched systematically on 30 October 2026. We repeat the searches every quarter, and new studies go through the same review.

Start here

Health, contaminant by contaminant: effects, who is at risk, evidence strength, legal limit vs health goal (20 contaminants)
When a barrier failed: 26 documented incidents, written as incident analyses
New: 201 sources added in the last 12 months, 9 studies still to report

Themes

Lead: Do home filters really take lead out? (15 sources: 3 strong, 8 moderate, 4 weak)
PFAS: Which filters take out PFAS ("forever chemicals")? (11 sources: 2 strong, 4 moderate, 5 weak)
Health effects on safe tap water: Does filtering already-safe city water make people healthier? (4 sources: 3 strong, 1 moderate, 0 weak)
Bacteria in filters: Do filters grow bacteria? (9 sources: 1 strong, 5 moderate, 3 weak)
Minerals and RO water: Is water without minerals (from reverse osmosis) a problem? (10 sources: 3 strong, 5 moderate, 2 weak)
Microplastics: Do filters remove microplastics, and does it matter? (11 sources: 2 strong, 4 moderate, 5 weak)
Silver in filters: Do silver-treated filters release silver? (5 sources: 1 strong, 3 moderate, 1 weak)
Filter life and late replacement: What happens when a cartridge is used too long, and how often do people change them? (17 sources: 2 strong, 9 moderate, 6 weak)
RO waste water and water rates: How much water does reverse osmosis send down the drain, and what does it cost? (12 sources: 5 strong, 4 moderate, 3 weak)
How much water people drink: How much water does a person drink and cook with? (5 sources: 5 strong, 0 moderate, 0 weak)
Electricity and bottled water: What do electricity and bottled water add? (9 sources: 2 strong, 4 moderate, 3 weak)
Showering: what you breathe and absorb: Does showering expose you to what is in your water? (17 sources: 5 strong, 11 moderate, 1 weak)
Legionella at home: Can your own hot-water system make you ill? (8 sources: 3 strong, 5 moderate, 0 weak)
Cooking with tap water: Does boiling make water safe? (9 sources: 3 strong, 6 moderate, 0 weak)
Infant formula and tap water: What matters when tap water goes into a bottle? (6 sources: 5 strong, 1 moderate, 0 weak)
Devices that bypass the gut: Nasal rinses, CPAP, humidifiers, dialysis, aquariums (8 sources: 2 strong, 5 moderate, 1 weak)
Can water add health?: Minerals, hydrogen, alkaline, silicon, lithium, fluoride: what the trials say (45 sources: 7 strong, 22 moderate, 15 weak)

How we searched

For each question we used a fixed set of search strings across scientific databases, government sites (EPA, CDC, WHO, BfR) and university pages. We included field studies in homes, lab studies with real tap water, trials, reviews and official datasets. We excluded manufacturer marketing and blogs. Where a database blocked automated access, we searched the open web, and we say so.