Quantitative microbiological risk assessments (QMRAs) combine pathogen concentrations in water with dose-response relationships and data reflecting potential exposure to estimate the risk of infection.
Data on water exposure are generally collected using questionnaires, but may also be determined from actual measurements of water ingested, or estimated from previously published data.  Respondents are asked to report the frequency and timing and location of exposures, detailed information about the amount of water swallowed and head submersion, and basic demographic characteristics such as age, gender, socioeconomic status and family composition.  Once sufficient data are collected and determined to be representative of the general population, they are usually fit with distributions, and these distribution parameters are then used in the risk assessment equations.  Monitoring data representing occurrence of pathogens, direct measurement of pathogen concentrations, or estimations deriving pathogen concentrations from indicator bacteria concentrations, are also fit with distributions.  Dose is calculated by multiplying the concentration of pathogens per volume by volume.  Dose-responses can also be fit with a distribution.