http://www.soest.hawaii.edu/GG/ASK/waterpol3.html
http://www.nyc.gov/html/dep/html/drinking_water/maplevels_wide.shtml
http://library.thinkquest.org/26026/Environmental_Problems/water_pollution_-_effects.html
http://tc.icwc-aral.uz/links/pollution.htm
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