One step in your quest to establish a causal relationship between benzene-contaminated home water and the patient’s condition would be to further investigate competing causes of low blood counts for this patient (e.g., drugs, radiation exposure, family history), keeping in mind that most cases of aplastic anemia are idiopathic. You would also need to explore the patient’s potential exposure to chemicals other than benzene that might cause hematologic disorders. Finally, assuming the patient’s condition is due to benzene exposure, you would need to weigh the significance of benzene sources other than the drinking water. For example, the patient is a diesel mechanic and most likely has inhalation and dermal exposure to gasoline (which contains benzene) at work. You would need to determine the amounts of benzene each source might have contributed to the patient’s exposure. (See answer number 1 above.)
For the patient in the case study, as for most exposure cases, it will not be an easy matter to establish causality, and there is no precedent for a person developing hematologic abnormalities from benzene in drinking water.