Fertilizers and chemicals are important contaminants of water and enter ground both directly and indirectly. In the case of Karst landscapes, the contaminated water infiltrates into the groundwater through underground streams or percolation.
Oil and gas spills also pose a serious problem for groundwater contamination as they can pollute aquifers near fracking zones and other oil extraction areas.
Animal feces are more of a problem in the modern age due to large-scale commercialized animal farms. Unless the waste from these facilities is controlled, it can runoff into fields and rivers and eventually seep into groundwater reserves.
B: China and India both have a population around 1.5 billion people so in total they have around 3 billion people combined! That is more than the continent of Africa and North America combined!
