Harvested Rainwater

Roof-collected rainwater used for drinking.

51Moderate burden · out of 100

Cleaner swapDrink mains water rather than untreated roof rainwater

How this score is built

100Start
81.6Chemical hazard 4 × 4.6−18.4
71.4Everyday exposure 3 × 3.4−10.2
51Persistence 8 × 2.6−20.8, then rounded to 51
ModerateThe band51 sits in 40–59.

What each input rests on

The three ratings behind the score, and the studies each rests on
Input	Rating	Evidence
Chemical hazard	4/10	Multiple studies link PFAS exposure to adverse immune outcomes in children, and dyslipidemia is the strongest metabolic outcome; cancer evidence is limited to manufacturing locations with extremely high exposures. A review of the pathways of human exposure to poly- and perfluoroalkyl substances (PFASs) and present understanding of health effects · J Expo Sci Environ Epidemiol 2019 DOI 10.1038/s41370-018-0094-1 · PMID 30470793 · Abstract · read 2026-10-02
Everyday exposure	3/10	In about 200 roof-harvested rainwater samples a year in Arizona (2017–2020), 28% exceeded the then US EPA advisory of 70 ng/L for PFOS plus PFOA, with a mean exceedance concentration of 189 ng/L. Organic micropollutants measured in roof-harvested rainwater from rural and urban environmental justice communities in Arizona · Sci Total Environ 2023 DOI 10.1016/j.scitotenv.2023.162662 · PMID 36898538 · Abstract · read 2026-10-02 Comparing global measurements with guideline levels, the authors conclude that PFOA and PFOS levels in rainwater often greatly exceed US EPA Lifetime Drinking Water Health Advisory levels. Outside the Safe Operating Space of a New Planetary Boundary for Per- and Polyfluoroalkyl Substances (PFAS) · Environ Sci Technol 2022 DOI 10.1021/acs.est.2c02765 · PMID 35916421 · Abstract · read 2026-10-02 Of 100 Adelaide household rainwater tanks, 1–4% exceeded Australian drinking-water health values for cadmium, iron, manganese, lead and arsenic; 67% of surveyed households drank the rainwater. From roof to tap: Emerging public health risks in harvested rainwater · J Environ Manage 2026 DOI 10.1016/j.jenvman.2026.130884 · PMID 42705031 · Abstract · read 2026-10-02
Persistence	8/10	All PFAS contain perfluoroalkyl moieties extremely resistant to environmental and metabolic degradation; most are non-degradable or transform into stable PFAS products, so they classify as very persistent under EU chemicals rules. The high persistence of PFAS is sufficient for their management as a chemical class · Environ Sci Process Impacts 2020 DOI 10.1039/d0em00355g · PMID 33230514 · Abstract · read 2026-10-02 After contaminated drinking water was replaced in Ronneby, Sweden, estimated mean serum half-lives were 5.3 years for PFHxS, 3.4 years for PFOS and 2.7 years for PFOA. Half-lives of PFOS, PFHxS and PFOA after end of exposure to contaminated drinking water · Occup Environ Med 2018 DOI 10.1136/oemed-2017-104651 · PMID 29133598 · Abstract, Results · read 2026-10-02

Ratings are editorial. A study listed here supports the rating; it did not compute it. How the index is built

What this means for you

The persistence rating is the standout concern here — these compounds linger in the body and environment for years. Rain carries PFAS: a 2022 global analysis in Environmental Science & Technology found PFOA and PFOS in rainwater often far above US EPA drinking-water advisory levels, and 28% of roof-harvested samples in an Arizona study exceeded the then 70 ng/L advisory. Roofs and tanks add their own: 1–4% of 100 Australian household tanks exceeded drinking-water health values for metals.

Evidence strength: moderate

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Lower-exposure choices

Reverse-Osmosis Filtered WaterMinimal · Water

Carbon-Filter Pitcher WaterLow · Water

All 8 water entries, highest burden first →