Environmental health risk assessment is a five step process by which you can integrate epidemiological information about linkage between an exposure and a disease to one where you can predict or characterise the risk given a set of exposure scenario. You will also need to integrate toxicological data to assess the relationship between dose of the toxin and the health effect. In the hazard idenification stage, we review results of epidemiological, toxicological and animal studies to identify the health effects that result from natural or experimental exposures of the toxin under consideration. In the dose-response stage, for the health effects we either assess a threshold level of no effect or lowest possible effect and based on the uncertainties around such estimations for humans, we derive a reference dose (Rfd) or a benchmark dose (BMD). If the health outcome is cancer, then we derive a slope parameter (slope factor) based on the dose-response curve. Based on measurements on the environment or exposure scenarios, we construct exposure profiles and identify model individuals who are exposed to the toxin in the exposure assessment stage. In the risk characterisation stage, we combine the exposure assessment information and either the Rfd or the slope parameter to estimate the risk of the disease with respect to the exposure. This could be in the form of comparison between Rfd and exposure based on the exposure data, or in terms of estimating the consumption of the media for a certain period of time before the health effects can be expected, or estimation of the probability of the cancer derived from exposure in terms of mg/kg body weight/day and slope factors. Based on these estimations, the mitigation efforts are then either continued watch or immediate action based on precautionary principles. We used three scenarios using three different compounds: fire-fighting foams that contain PFOA to contaminate drinking water, inorganic arsenic that naturally occurs in some parts of the world and their potential to cause cancer and non-cancerous health effects, and chlorine that was recently added to the water supply systems of Christchurch city to derive estimates of risk. The results of these three desktop applications of EHRA suggest that with existing data bases and information sources, it is possible to conduct desktop EHRA that can elucidate environmental health risks in different contexts.