PFAS Exposure Risk Calculator
Overview: What This PFAS Calculator Estimates
This page provides an educational tool to estimate your potential intake of per- and polyfluoroalkyl substances (PFAS) from drinking water and to compare that intake to an example health-based reference level. It focuses only on ingestion from drinking water and expresses exposure as a hazard quotient (HQ) relative to a chosen reference dose.
The calculator is intended for homeowners, tenants, and community members who have measured or estimated PFAS levels in their tap or well water and want a simple way to understand how those concentrations, combined with daily water intake and body weight, might relate to commonly used risk metrics in environmental health.
What Are PFAS?
PFAS (per- and polyfluoroalkyl substances) are a large family of synthetic chemicals used for their resistance to heat, water, and oil. They are found in products such as non-stick cookware, stain-resistant textiles, some food packaging, and certain firefighting foams. Because PFAS are highly persistent and do not readily break down, they are sometimes called “forever chemicals.”
PFAS can enter drinking water through industrial discharges, use of firefighting foams at training sites, wastewater treatment plant discharges, or leaching from landfills. Once PFAS reach groundwater or surface water sources, they can be difficult and costly to remove. Many communities have discovered PFAS contamination only after targeted testing became available.
Scientific studies have associated elevated PFAS exposure with a range of potential health effects, including:
- Changes in cholesterol levels
- Certain immune system effects, including reduced vaccine response
- Thyroid hormone disruption
- Developmental effects in fetuses and infants
- Increased risk of some cancers for specific PFAS compounds
Regulatory agencies such as the U.S. Environmental Protection Agency (EPA) and various national and regional health authorities are developing and updating health-based guidelines and drinking water standards for several PFAS. The numbers used in this calculator are illustrative and do not replace official guidance.
How the Calculator Works
The calculator estimates the average daily intake of PFAS from drinking water on a body-weight basis and then compares that value to an example reference dose (RfD). The RfD is a benchmark intake level (per kilogram of body weight per day) that is considered, based on current science, to be unlikely to cause adverse health effects over a lifetime of exposure. Different agencies may use different RfDs depending on the compound and methodology.
In this tool, you provide three inputs:
- PFAS concentration in water (C): in nanograms per liter (ng/L)
- Daily water intake (W): in liters per day (L/day)
- Body weight (B): in kilograms (kg)
Using these values, the calculator performs two main steps:
- Estimate your daily PFAS intake per kilogram of body weight.
- Compare that intake to an example RfD (0.02 ng/kg/day) using a hazard quotient.
Formulas Used
First, the daily mass of PFAS ingested from water is the product of concentration and volume:
Daily PFAS mass (ng/day) = C × W
Next, the calculator converts this to an intake rate per kilogram of body weight by dividing by B:
I = (C × W) / B, where I has units of ng/kg/day.
In mathematical notation, the same relationship can be represented as:
The calculator then compares this intake to an example reference dose, denoted here as RfD. For illustration, the tool uses:
RfD = 0.02 ng/kg/day
The hazard quotient is the ratio of your estimated intake to the reference dose:
HQ = I / RfD
When HQ = 1, the estimated intake equals the reference dose. When HQ < 1, the intake is below the reference dose, and when HQ > 1, it exceeds the example benchmark.
Interpreting the Hazard Quotient (HQ)
The hazard quotient is a screening-level indicator commonly used in environmental risk assessment. It is not a direct prediction of disease, but rather a way to compare an estimated exposure to a health-based guideline. Values are typically interpreted as follows:
| HQ range | Screening interpretation |
|---|---|
| < 1 | Estimated intake is below the example reference dose. At this screening level, risk is generally considered low, though it is not zero, and sensitive individuals may still wish to consult local guidance. |
| 1–10 | Estimated intake is above the example reference dose. This suggests that further evaluation, mitigation measures (such as treatment or alternative water sources), or consultation with local water and health authorities may be appropriate. |
| > 10 | Estimated intake is well above the example reference dose. This may indicate a need for prompt follow-up, including confirmatory testing of water, discussion with local authorities, and, where possible, use of safer alternative water until more information is available. |
These categories are generic examples. Different agencies or risk assessors may use different ranges, terminology, or decision thresholds. Always compare your results with current guidance from trusted public health or environmental agencies in your jurisdiction.
Worked Example (Hypothetical)
The following example shows how to use the calculator and how to interpret the result. These numbers are illustrative only and do not represent a recommended or “safe” level.
Example 1: Adult
Suppose an adult has:
- PFAS concentration in tap water, C = 10 ng/L
- Daily drinking water intake, W = 2 L/day
- Body weight, B = 70 kg
Step 1: Calculate intake per kilogram of body weight.
I = (10 ng/L × 2 L/day) / 70 kg = 20 / 70 ≈ 0.286 ng/kg/day
Step 2: Compare to the example reference dose, RfD = 0.02 ng/kg/day.
HQ = 0.286 / 0.02 ≈ 14.3
Interpretation: An HQ of about 14 would fall into the “> 10” category in the table above, indicating that this hypothetical exposure is well above the example reference dose and that further evaluation or action could be warranted.
Example 2: Child
Children often drink more water per kilogram of body weight than adults, so it is useful to consider an example:
- PFAS concentration in tap water, C = 5 ng/L
- Daily drinking water intake, W = 1 L/day
- Body weight, B = 20 kg
Step 1: Intake per kilogram of body weight.
I = (5 ng/L × 1 L/day) / 20 kg = 5 / 20 = 0.25 ng/kg/day
Step 2: Hazard quotient.
HQ = 0.25 / 0.02 = 12.5
Interpretation: Even though the water concentration is lower than in the adult example, the higher intake per kilogram of body weight leads to a relatively high HQ for this hypothetical child.
These examples highlight why exposure assessments typically adjust for body weight and why children and other sensitive groups may require special consideration.
Key Assumptions and Limitations
It is important to understand what this tool does not do. The calculator makes several simplifying assumptions that limit how precisely it can describe real-world risk.
- Single, constant water concentration: The tool assumes that the PFAS concentration in your drinking water is accurately known and stable over time. In reality, concentrations may vary by season, well use, treatment effectiveness, or blending of water sources.
- Average daily intake only: The calculation uses your typical daily volume of drinking water. It does not distinguish between short-term peaks and long-term averages, and it does not address acute (very short-term) exposures.
- Single-compound or “total PFAS” simplification: Many water test results report one or a few specific PFAS (such as PFOA or PFOS), while others provide a “total PFAS” estimate. Different PFAS compounds can have different toxicities, and combining them into one number is a simplification.
- No body burden modeling: PFAS can persist in the body for years. This calculator estimates daily intake only; it does not model how PFAS accumulate or are eliminated over time, nor does it estimate blood or tissue concentrations.
- Example reference dose: The RfD value of 0.02 ng/kg/day is used here as an example, based on recent toxicological assessments for highly scrutinized PFAS. Regulatory agencies may publish different numbers, and those values may change as new data emerge.
- Population variability and susceptibility: The tool does not account for individual health status, pregnancy, age, genetic differences, co-exposures to other chemicals, or underlying medical conditions that may change susceptibility to PFAS.
- Other exposure pathways: Only drinking water ingestion is included. PFAS exposure can also occur via food, indoor dust, consumer products, and occupational activities, which are outside the scope of this calculator.
Because of these limitations, the HQ output should be treated as a screening-level indicator, not a precise prediction of health effects.
Comparison: What the Calculator Covers vs. Real-World Risk
The table below contrasts the simplified approach used in this tool with more comprehensive risk assessments that may be conducted by regulatory agencies or specialized consultants.
| Aspect | This calculator | Comprehensive risk assessment |
|---|---|---|
| Exposure pathways | Drinking water ingestion only | Multiple pathways: water, food, inhalation, dust, consumer products, occupational exposures |
| PFAS compounds | Single numeric input (specific compound or total PFAS) | Compound-specific analyses, mixture assessments, and sometimes multiple endpoints |
| Time dimension | Average daily intake at one point in time | Short-term and lifetime exposures, temporal trends, and historical data |
| Body burden and kinetics | No explicit modeling of accumulation or elimination | Pharmacokinetic or physiologically based models for blood and tissue concentrations |
| Health outcomes | Hazard quotient relative to an example RfD | Quantitative or qualitative characterization of specific health endpoints and uncertainties |
| Uncertainty analysis | Not explicitly quantified | Formal uncertainty factors, sensitivity analyses, and scenario comparisons |
| Regulatory context | Informational only, not tied to any specific standard | Aligned with current regulations, guidance values, and jurisdiction-specific requirements |
When to Seek Professional Help
If this calculator suggests an HQ at or above 1, or if you already have concerns about PFAS in your water, consider the following actions:
- Review guidance from your national or regional environmental or public health agency (for example, the U.S. EPA or your state/provincial health department).
- Contact your local water utility or water authority to request information on PFAS monitoring and treatment.
- Discuss any health concerns with a qualified healthcare professional, especially for pregnant people, infants, or individuals with existing health conditions.
- Consult independent, certified laboratories or environmental professionals if you need confirmatory testing or a more detailed risk assessment.
Disclaimer
This calculator is provided for informational and educational purposes only. It does not provide medical, legal, or regulatory advice and should not be used as the sole basis for health or financial decisions. The example reference dose and interpretation categories used here may differ from values and frameworks used by official agencies.
Always consult qualified health professionals, environmental specialists, or relevant regulatory authorities for advice that is specific to your situation, jurisdiction, and the most current scientific evidence.