Contamination

Bioremediation is the process by which microbes (generally bacteria) or plants transform a harmful water contaminant into a non-harmful substance, much as we turn sugar into carbon dioxide
The air pressure in the ground around most houses is often greater than the air pressure inside the house. Thus, air tends to move from the disturbed zone, resulting from its construction, into the house through openings in the house's foundation.
Information on pesticides and herbicides and on nutrients is available from the USGS National Water-Quality Assessment Program 
Different treatment is used depending on the source of your water. Ground water taken from wells has been filtered through rocks, so it is usually quite free of particles.
There are many different kinds of treatments depending on what contaminant is in the water. Biological contamination is usually treated by heat (boiling) or by filtration.
Yes, it is called reclaimed wastewater, though its use is limited. Before you start to feel ill, no, it is not used further down the line as drinking water. It is most often used for irrigation and for water parks and golf courses.
Saline water has some uses. In 2000, the U.S. used about 62 billion gallons per day of saline water, which was about 15 percent of all water used.
You can get an idea as to how concerned you should be about radon in your house by learning about the geology of the site and its radon potential.
It is possible that there may have been a mutation in the virus that is causing a higher number of species to be affected this year. There is currently no evidence of significant mutation in the U.S.
Many, but not all, fish kills in the summer result from low concentrations of dissolved oxygen in the water. Fish, like all other complex life forms, need oxygen to survive. They get theirs in the form of oxygen gas dissolved in the water.