Will Natural Burial contaminate water sources?
The short answer is "No."

A concern sometimes raised about natural burial practices is water contamination. Because the body is placed in the earth in a biodegradable casket or shroud with no concrete vault, some people worry that the residue from a naturally decomposing body will leach through the soil to contaminate wells or other bodies of water. The Green Burial Council (GBC) states that “no contamination has been reported from or near any green cemeteries in the U.S., Canada, Great Britain or Australia since their inception in 2003.” As long as best management burial practices are followed, the potential for contamination of drinking water due to body decomposition is not substantiated by any studies at this time.  [from The Science Behind Green and Conventional Burial in Lay Terms  ] Best management practices include setback parameters from all known water sources, including water table depths, ground water and aquifers, and recommended depths for burial based on soil type and typography. 

The Pan American Health Organization (PAHO) concurs, stating: “There is little evidence of microbiological contamination of groundwater from burial…Microorganisms involved in the decay process (putrefaction) are not pathogenic.” One significant advantage of natural burial grounds is the lack of runoff into water sources of herbicides, pesticides and fertilizers which conventional burial ground typically use in abundance.