Geoengineeringwatch has these guidelines for water testing, which have been posted on there since January 2010 http://www.geoengineeringwatch.org/html/watertesting.html (http://archive.is/tskGA) Some of the advice is good. Except: Multiple jars placed on the ground in the rain are obviously going to get groundwater splashed in them in heavy rain, so will be even more contaminated with dirt. Mason jar lids are often made from aluminum Shaking a jar will ensure that all the dust on the surface of the jar (not from rain) will be mixed with the rain. Any jar left out for more that a few hours will get dust on it. Adding sediment from a pond is the exact opposite of what you want. Sediment is dirt. That's aluminum. You have zero control over how much ends up in your sample. So the results will be both high in aluminum, and meaningless.