Farming overspray and rainfall collection

In another topic Benefits of rainfall collection
questions about overspray from cropping and its potential effect on rainfall collection was raised.
From; water tank health
I found this "Pesticides – agricultural pollution
Use of pesticides and potential drift from agricultural areas has been the subject of increasing public concern, and one of the issues commonly raised has been potential contamination of roofs used as catchments for rainwater tanks. There have been complaint investigations but pesticides are rarely detected and, where they are, concentrations are well below health-related guideline values (South Australian
Department of Human Services, unpublished results).
In surveys of rainwater quality in rural areas, most samples did not contain detectable concentrations of pesticides (Victorian Department of Natural Resources and Environment 1997; Fuller et al. 1981; Paskevich 1992; New South Wales Environment Protection Authority and Northern Districts Public Health Unit 1996; Chapman et al. 2008). Endosulfan, profenofos, chlorpyrifos and dieldrin were detected in some samples, but all at concentrations well below health-related guideline values cited in the ADWG.
If in doubt about the use of pesticides in a particular area, advice should be sought from the relevant agriculture, environmental health or environment protection agency.
Slow-combustion heaters
Concerns have been expressed about the potential impact of emissions from slow combustion wood fires on rainwater collected in domestic tanks. Public complaints have ranged from reports of a slight burnt wood taste to tainting with creosote. However, in a survey of rainwater collected from roofs incorporating wood heater flues, polyaromatic hydrocarbon (found in combustion products) concentrations did not exceed guideline values in the ADWG (Victorian Department of Natural Resources and Environment 1997).

From;A study in Iowa
"Results
Detection rates for individual herbicides ranged from 0% for metribuzin and cyanazine to 95% for 2,4-D (Table 1).
One or more of the six agricultural herbicides were detected in 28% of homes, whereas the four long-term–use herbicides were detected in 43% of homes.
A few herbicides with high use (e.g., atrazine) were not detected frequently. Metolachlor was the most frequently detected herbicide in the agricultural herbicide group, whereas dicamba was the most frequently detected among the long-term–use herbicides.
All homes with detections of one or more of the agricultural and long-term–use herbicides also had detections of 2,4-D.
The concentration of 2,4-D was > 2-fold higher than any other herbicide. Herbicides with the highest geometric mean concentrations were 2,4-D, dicamba, pendimethalin, and acetochlor......."