The Vera Purity Index.
A composite score from 0 to 100 that rates bottled water quality across seven independently weighted dimensions. Designed to go beyond regulatory compliance and reflect what the peer-reviewed literature suggests is optimal for human health.
How it starts
Every product starts at 50, representing a baseline water with no distinguishing qualities in either direction. Points are added or subtracted based on seven categories of evidence. The final score is clamped between 0 and 100. This lower starting point makes high scores harder to achieve and the scale more honest overall.
Score tiers
1. Contaminant Safety
-40 to +15Evaluates the concentration of known chemical contaminants against two separate benchmarks: the U.S. EPA Maximum Contaminant Levels (MCLs), which are the legal limits, and the Environmental Working Group (EWG) Health Guidelines, which are set at stricter levels based on one-in-a-million cancer risk or no-observed-adverse-effect levels.
Why two benchmarks? EPA MCLs are set with economic and technological feasibility in mind, not purely on health grounds. EWG guidelines are derived solely from health-protective science, and for many contaminants are substantially lower than the legal limits.
Scoring logic
- Exceeding an EPA MCL: severe penalty scaled by log-ratio and toxicity weight
- Exceeding an EWG guideline: moderate penalty scaled by ratio and toxicity
- Approaching an EWG guideline (50-100% of limit): minor penalty
- Below 50% of EWG guideline: no penalty
- All below 10% of EWG: +15 | Below 25%: +10 | Below 50%: +5
Penalty formulas & log scaling
EPA MCL breach
penalty = weight x (5 + log10(measured / limit) x 10)
EWG guideline breach
penalty = weight x (2 + log10(measured / guideline) x 5)
The 40-point cap (dashed line) prevents any single contaminant from dominating the total score. Log scaling compresses extreme values: 10x the limit only adds ~30 pts more than being exactly at the limit.
Worked examples
10 ppb (exactly at limit)
ratio = 1.0 | log10(1.0) = 0.000
penalty = 3 x (5 + 0.000 x 10) = 15 pts
20 ppb
ratio = 2.0 | log10(2.0) = 0.301
penalty = 3 x (5 + 0.301 x 10) = 24 pts
100 ppb
ratio = 10.0 | log10(10.0) = 1.000
penalty = 3 x (5 + 1.000 x 10) = 40 pts
3 ppb (EWG guideline = 1 ppb)
ratio = 3.0 | log10(3.0) = 0.477
penalty = 3 x (2 + 0.477 x 5) = 13.2 pts
Why logarithmic, not linear? A linear penalty would make arsenic at 10x the limit cost 10x more than being exactly at the limit. The log scale compresses this: going from 1x to 10x the limit only adds ~30 points (15 to 45, capped at 40). This prevents a single extreme outlier from collapsing the entire score, while still penalising dangerous exceedances heavily.
Toxicity weighting
| Contaminant | Weight | Basis |
|---|---|---|
| Lead, Arsenic | 3.0 | IARC Group 1 carcinogens; no safe threshold |
| Chromium-6, Uranium | 2.5 | Known/probable human carcinogens |
| PFAS compounds | 2.5 | Persistent endocrine disruptors; EPA 2024 MCL at 4 ppt |
| Mercury, Bromate, THMs, HAAs | 2.0 | IARC Group 2A/2B; cardiovascular/renal toxicity |
| Nitrate, Nitrite, Fluoride, Cadmium | 1.5 | Developmental toxicants; dose-dependent risk |
| Barium, Copper, Chlorine | 0.5-1.0 | Lower systemic toxicity at typical concentrations |
Key references
2. Transparency & Testing
-20 to +15A brand's willingness to publish independent test data is itself a signal of quality and accountability. This category rewards comprehensive testing and published results.
Required test categories (9 total)
Scoring logic
| Condition | Score |
|---|---|
| No test data at all | -10 |
| Some data (lab reports or minerals, no formal categories) | -5 |
| Partial coverage (<50% of required categories) | -5 |
| Moderate coverage (50-79%) | -3 |
| Strong coverage (80-99%) | +3 |
| Full coverage (all 9 categories) | +7 |
| Published lab reports (1 report) | +3 |
| Published lab reports (2+ reports) | +5 |
| Recent reports (<2 years old) | +3 |
| Third-party laboratory verification | +5 |
| NSF International certification | +4 |
Key references
- NSF International. Bottled Water Certification.
- U.S. EPA. Consumer Confidence Reports Rule. 40 CFR Part 141.
- Gleick, P.H. Bottled and Sold: The Story Behind Our Obsession with Bottled Water. Island Press (2010).
3. Source & Treatment
-10 to +10The origin of water and how it is processed before bottling meaningfully affects its purity, mineral integrity, and exposure to industrial contamination.
Source adjustments
| Source Type | Score | Rationale |
|---|---|---|
| Spring / Aquifer | +5 | Natural filtration through geological substrate |
| Deep well / Glacier / Iceberg | +3 | Remote, low-exposure sources with natural mineral content |
| Rain / Atmospheric | -3 | Susceptible to atmospheric pollutant deposition |
| Municipal (tap-sourced) | -5 | Pre-treated municipal supply; chemical disinfectants may persist |
| Unknown / undisclosed | -10 | Lack of provenance is itself a transparency concern |
Treatment adjustments
| Treatment | Score | Rationale |
|---|---|---|
| UV disinfection | +3 | Pathogen inactivation without chemical residues |
| Ozonation | +2 | Effective disinfection; breaks down to oxygen |
| Activated carbon filtration | +2 | Reduces VOCs, chlorine, and taste compounds |
| Reverse osmosis | 0 | Effective purification but removes beneficial minerals |
| Chlorination | -2 | May leave residual trihalomethanes and chlorine |
| Chloramine | -3 | Harder to remove; associated with disinfection byproduct formation |
Key references
- WHO. Guidelines for Drinking-water Quality, 4th ed. with 1st Addendum. Geneva: WHO (2022).
- Richardson, S.D. et al. "Occurrence, genotoxicity, and carcinogenicity of regulated and emerging disinfection by-products." Mutat Res 636(1-3): 178-242 (2007).
4. Packaging & Materials
-10 to +5Container material is a major but often overlooked determinant of bottled water quality. Plastics can leach monomers, plasticisers, and other chemicals into water, particularly under heat or UV exposure.
| Material | Score | Rationale |
|---|---|---|
| Glass | +5 | Chemically inert; zero leaching |
| Stainless steel | +5 | Inert, durable; no documented leaching |
| PLA bioplastic | -1 | Compostable; low leaching risk but limited data |
| Cardboard / Tetra Pak | -2 | Low leaching; some adhesive layer concerns |
| Aluminum | -3 | Typically lined with epoxy/BPA-based coating |
| HDPE (#2) | -3 | Lower leaching than PET; used for large-format jugs |
| Polypropylene (#5) | -4 | Moderate leaching at elevated temperatures |
| Polyethylene | -5 | Variable additive packages; moderate risk |
| PET (#1) | -7 | Leaches antimony, acetaldehyde; risk increases with heat/reuse |
| Polystyrene (#6) | -8 | Leaches styrene monomer; IARC Group 2B carcinogen |
| PVC (#3) | -10 | Leaches vinyl chloride, phthalates, lead stabilisers |
Certified microplastic-free: penalty halved
BPA-free certification on aluminum: +2
Key references
- Koivisto, A.J. et al. "Quantitative chemical risk assessment for migration of substances from plastic food contact materials." Food Chem Toxicol (2021).
- Westerhoff, P. et al. "Antimony leaching from PET plastic used for bottled drinking water." Water Res 42(3): 551-556 (2008).
- IARC. Monograph 101: Styrene (2013).
- EFSA. Bisphenol A (BPA) re-evaluation. EFSA Journal (2023).
5. PFAS & Emerging Contaminants
-10 to +5PFAS and microplastics represent two of the most significant emerging concerns in drinking water science. Unlike legacy regulated contaminants, these were not routinely tested for until recently, anda brand's decision to test and disclose results is itself meaningful.
PFAS scoring
| Result | Score | Rationale |
|---|---|---|
| Not tested | 0 | Neutral; no data either way |
| Non-detect | +5 | Demonstrates active quality management |
| Detected, below EWG guideline | -3 | Concerning presence of persistent chemicals |
| Detected, above EWG guideline | -10 | Significant health risk; EPA 2024 MCL = 4 ppt |
Microplastics scoring
| Result | Score |
|---|---|
| Not tested | 0 |
| Non-detect | +2 |
| Detected, <=10 particles/L | 0 |
| Detected, >10 particles/L | -5 |
Why PFAS matters
PFAS are synthetic fluorinated compounds persistent in the environment and the human body, linked to thyroid disruption, immune suppression, reproductive toxicity, and several cancers. In 2024, the EPA established the first-ever federal MCL at 4 parts per trillion (ppt) for PFOA and PFOS.
Why microplastics matter
A 2018 Orb Media analysis found microplastic contamination in 93% of tested bottled water brands globally. A 2021 study estimated humans ingest 39,000-52,000 microplastic particles annually. Toxicological implications include inflammation, endocrine disruption, and carriage of adsorbed chemical pollutants.
Key references
- U.S. EPA. PFAS National Primary Drinking Water Regulation (April 2024).
- Olsen, G.W. et al. "Half-life of serum elimination of PFOS, PFHxS, and PFOA." Environ Health Perspect 115(9): 1298-1305 (2007).
- Mason, S.A. et al. "Synthetic polymer contamination in bottled water." Orb Media (2018).
- Cox, K.D. et al. "Human consumption of microplastics." Environ Sci Technol 53(12): 7068-7074 (2019).
- Ragusa, A. et al. "Plasticenta: First evidence of microplastics in human placenta." Environ Int 146: 106274 (2021).
6. Mineral Profile
-10 to +20The only category that can award more points than it deducts, reflecting the growing evidence that mineral-rich water confers measurable health benefits beyond simple hydration. Each mineral is scored individually against evidence-based ranges, followed by a diversity bonus.
Calcium
Associated with reduced cardiovascular mortality and improved bone mineral density. WHO recommends a provisional minimum of 20 mg/L, with strongest cardiovascular benefit at >50 mg/L.
| Calcium (mg/L) | Score | Label |
|---|---|---|
| >= 50 | +4 | High — supports bone & cardiovascular health |
| 20 - 49 | +3 | Good |
| 10 - 19 | +1 | Adequate |
| 5 - 9 | 0 | Neutral |
| < 5 | -1 | Very low |
Magnesium
Essential cofactor in over 300 enzymatic reactions. Low dietary magnesium is among the most consistent risk factors for cardiovascular disease. Water-borne magnesium is highly bioavailable relative to food sources.
| Magnesium (mg/L) | Score | Label |
|---|---|---|
| >= 30 | +4 | High — strong cardiovascular & muscle benefit |
| 10 - 29 | +3 | Good — supports cardiovascular health |
| 5 - 9 | +1 | Adequate |
| < 5 | -1 | Very low — associated with higher cardiovascular risk |
| > 125 | -2 | Very high — laxative effect risk |
Silica
The PAQUID cohort study (7,598 French adults, 15 years) found silica intake >= 10 mg/L was significantly associated with reduced dementia incidence. Silicon-rich water (>= 30 mg/L) measurably reduced urinary aluminium excretion, suggesting protective role against aluminium neurotoxicity.
| Silica (mg/L) | Score |
|---|---|
| >= 30 | +4 |
| 10 - 29 | +3 |
| 5 - 9 | +1 |
Bicarbonate
Primary physiological pH buffer. Waters with >= 150 mg/L have been associated with improved acid-base balance and reduced cardiovascular risk markers in controlled trials.
| Bicarbonate (mg/L) | Score |
|---|---|
| >= 150 | +2 |
| 50 - 149 | +1 |
Sodium
While water is a minor sodium source for most people, those on sodium-restricted diets should monitor water sodium. WHO's palatability guideline of 200 mg/L is aesthetic only.
| Sodium (mg/L) | Score | Label |
|---|---|---|
| <= 20 | +2 | Naturally low |
| 21 - 50 | +1 | |
| > 100 | -1 | Elevated |
| > 200 | -3 | Exceeds WHO palatability guideline |
Fluoride
Exhibits a classic hormetic dose-response: low concentrations protect dental enamel; above certain thresholds it causes fluorosis. The 2015 U.S. Public Health Service optimal level is 0.7 mg/L.
| Fluoride (mg/L) | Score | Label |
|---|---|---|
| <= 0.3 | +1 | Very low; negligible fluorosis risk |
| 0.3 - 1.0 | 0 | Near optimal |
| 1.0 - 1.5 | -1 | Above CDC optimal |
| 1.5 - 2.0 | -3 | Exceeds WHO health guideline |
| 2.0 - 4.0 | -4 | Dental fluorosis risk |
| > 4.0 | -6 | Exceeds EPA MCL; skeletal fluorosis risk |
pH
The health significance of pH is frequently misunderstood. WHO's 6.5-8.5 guideline is aesthetic, not health-based. Commercially marketed "alkaline water" (pH 8-10, artificially raised) has been found in RCTs to produce no clinically meaningful health effect.
| pH | Score | Note |
|---|---|---|
| < 5.5 | -5 | Significant dental erosion risk |
| 5.5 - 6.5 | -3 | Mild erosion risk |
| 6.5 - 9.5 | 0 | Optimal range; no evidence of harm or benefit |
| > 9.5 | -3 | Extreme alkalinity; case reports of harm |
| > 8.5, artificially alkalised | -2 | No evidence of benefit |
TDS (Total Dissolved Solids)
A summary measure of all dissolved minerals, used as a cross-check signal rather than a primary determinant.
| TDS (ppm) | Score | Note |
|---|---|---|
| < 20 | -4 | Essentially distilled; mineral-free |
| 20 - 50 | -2 | Very low; heavily filtered or RO |
| 50 - 100 | 0 | |
| 100 - 600 | +1 | WHO "excellent" to "good" palatability range |
| 600 - 1200 | -1 | WHO "fair" palatability |
| > 1200 | -2 | WHO "unacceptable"; high dissolved solids |
Mineral Diversity Bonus
The combination of calcium, magnesium, silica, and bicarbonate likely produces synergistic cardiovascular and metabolic benefits beyond any single mineral in isolation.
| Minerals in beneficial range | Bonus |
|---|---|
| 4+ minerals | +5 |
| 3 minerals | +3 |
| 2 minerals | +1 |
Remineralisation caveat: Products artificially remineralised after reverse osmosis receive 50% of their calculated mineral score. While resulting concentrations may be identical to a natural spring, the bioavailability of naturally occurring mineral complexes is superior to post-processing additions.
Key references
- WHO. Calcium and Magnesium in Drinking-Water (2009).
- Rosenlund et al. (2022) — Calcium in drinking water & cardiovascular mortality.
- Catling et al. (2008) — Systematic review: water hardness & cardiovascular disease.
- Rylander (1996) — Environmental magnesium deficiency as cardiovascular risk factor.
- Rosanoff et al. (2012) — Suboptimal magnesium status in the United States.
- Rondeau et al. (2009) — Aluminium, silica & risk of Alzheimer's disease (PAQUID cohort).
- Davenward et al. (2013) — Silicon-rich mineral water & aluminium burden in Alzheimer's.
- U.S. Public Health Service Recommendation (2015) — 0.7 mg/L optimal fluoride level.
- WHO. Fluoride Background Document (GDWQ 2022).
- Aoi et al. (2012) — RCT: alkaline water, microbiota & glucose (no effect found).
- EFSA (2016) — Scientific opinion on alkaline water health claims.
- AJEM (2023) — Case report: alkalosis from sustained high-pH water intake.
- Bernstein & Willett (2010) — Trends in urinary sodium excretion.
- Kozisek (2005) — Health risks from drinking demineralised water (WHO).
- Raju (2014) — TDS and groundwater quality indicators.
- WHO. TDS Background Document (WHO/SDE/WSH/03.04/16).
- WHO. pH Background Document (WHO/SDE/WSH/07.01/1).
7. Brand Track Record
-15 to +5Track Record measures one thing: does this brand have a clean legal and safety history? It is deliberately kept separate from Transparency & Testing, which rewards published lab data. Previously, this category gave bonus points for multiple lab reports — but that double-counted with Transparency. Now the two categories measure completely different signals:
Transparency
Do you publish your testing data?
Track Record
Do you have a clean legal/safety history?
| Factor | Adjustment |
|---|---|
| Product recall (1 event) | -5 |
| Multiple recalls | -10 |
| California Prop 65 warning | -5 |
| Verified legal action (contamination / fraud) | -5 |
| Clean record (zero recalls, lawsuits, or Prop 65 warnings) | +5 |
Recalls sourced from U.S. FDA Enforcement Reports. Prop 65 listings from California OEHHA. Legal actions included only with verifiable source URL.
How Scoring Works
AI Research & Human Verification
The Automated Pipeline
When you scan a product that isn't yet in our database, Vera's research pipeline activates automatically. Within 30–60 seconds, the system runs the following steps in parallel:
AI Knowledge Recall— Claude (Anthropic)
Queried for everything it knows about the product: source location, mineral composition, pH, TDS, treatment methods, packaging, testing history, and brand track record. For well-known brands, Claude’s training data often contains accurate mineral profiles sourced from brand documentation, regulatory filings, and scientific literature.
Web Search— Tavily
Eight independent searches run simultaneously, targeting official lab reports, water quality certificates, mineral analyses, regulatory databases (EWG, NSF), consumer watchdog coverage, and legal records. Discovered PDF reports and quality pages are fetched directly.
Structured Extraction— Gemini (Google)
All gathered content is passed to Gemini, which extracts a standardised data structure covering over 40 fields: mineral concentrations, contaminant levels, source coordinates, treatment methods, packaging type, PFAS testing status, microplastic data, and track record events.
Scoring— Vera Purity Index Engine
The extracted data is passed through the scoring engine, which calculates the score across all seven categories using the methodology described above.
Storage— Instant availability
The product profile, mineral data, contaminants, lab report links, and score are stored and immediately available to all users.
This entire process runs without human involvement.
The Confidence Score
Because the automated pipeline relies on AI and publicly available web data, not every product is equally well-documented. A niche regional brand with no English-language web presence will naturally have less verifiable data than a global brand with published annual quality reports and NSF certification.
Every AI-researched product carries a confidence score from 0 to 100, displayed on the report. This score is self-assessed by the AI extraction model based on the quality and diversity of sources it was able to draw from:
Multiple corroborating official sources — PDFs, regulatory databases, NSF/EWG records — with specific numeric values cross-checked across sources.
Good web source coverage combined with AI knowledge; most key fields populated with real, verifiable values.
Primarily AI training knowledge with limited or no independent web verification; figures are plausible but unconfirmed.
Limited data available; most fields estimated or inferred; treat results with caution.
Almost no verifiable data found; product is largely unknown to public databases.
A low confidence score does not mean the water is unsafe — it means we simply don't have enough data to evaluate it thoroughly. In these cases, the absence of transparency is itself reflected in the Transparency & Testing category score.
The Verified Badge
The Verified badge is awarded only after a member of the Vera team has manually reviewed the product report against primary sources. Verification involves:
- Cross-checking mineral and contaminant values against the brand’s official published documents or third-party lab reports
- Confirming the source, treatment methods, and packaging type
- Reviewing any flagged concerns (recalls, lawsuits, Prop 65 listings) against primary records
- Adjusting the score if the automated extraction produced inaccuracies
An AI-researched report without the Verified badge should be treated as a best-effort estimate, not a certified finding. The confidence score gives you a signal of how much to trust it. A report with 85% confidence and coherent mineral data is likely reliable. A report with 35% confidence should be read with healthy scepticism until verified.
We are progressively verifying products in the database, prioritising those with the most scans and lowest confidence scores. If you believe a report contains an error, you can flag it directly from the product page and our team will review it.
A Note on Limitations
No automated system is perfect. AI models can hallucinate specific values — particularly for obscure products with little web presence. Web searches may surface outdated lab reports. Brands occasionally update their source, treatment process, or formulation without public announcement.
We build these limitations directly into the scoring system: brands that do not publish test data receive transparency penalties, and products without verified human review carry the confidence score as an explicit uncertainty signal. Our goal is not to create false precision, but to give you the most honest and useful picture of water quality that current data allows.
Limitations & Disclosures
The VPI is a scoring model, not a regulatory certification. It synthesises available published evidence and disclosed product data.
Where brands do not publish contaminant test data, scores reflect that absence of transparency rather than confirmed quality.
Mineral and contaminant values reflect conditions at the time of last available testing. Water quality can vary between batches, seasons, and production facilities.
The VPI does not test products independently. Where brands are found to have published inaccurate data, scores will be updated.
Vera Purity Index methodology current as of 2026. Last reviewed February 2026.