@book{31,
	author = {Letterman, Raymond D. and American Water Works Association.},
	title = {Water quality and treatment :},
	publisher = {McGraw-Hill,},
	year = {c1999.},
	address = {New York :},
	edition = {5th ed.},
	url = {http://www.loc.gov/catdir/bios/mh041/99049136.html}
}