13-00CO Title: Iceberg Caption: Water molecules superimposed onto an iceberg. Notes: Hydogen bonding occurs between water molecules in ice.

13-02 Title: The Hydrological Cycle Caption: Diagram illustrating the water cycle. Notes: Water is necessary for life on our planet.

13-02-03UN Title: Waterborne Disease Caption: Fluorescent image of the microorganisms responsible for the Milwaukee water supply contamination in 1993. The organisms are less than 0.003 inches in diameter. Notes: Contamination of water supplies by microorganisms from human wastes can cause typhoid fever, dysentery, and cholera.

13-05 Title: Water Treatment Caption: Diagram illustrating the process for water purification at a municipal water treatment plant. Notes: Water purification is a multistep process.

13-06 Title: Wastewater Treatment Caption: Diagram illustrating the steps in wastewater treatment at a sewage plant. Notes: Wastewater treatment is a multistep process.

13-07 Title: Activated Sludge Method Caption: Diagram illustrating the process for treating wastewater by the activated sludge method. Notes: Methods for wastewater treatment involve several steps.

13-TB02 Title: Table 13.2 Some Substances Found in Natural Waters Caption: A list of compounds and elements found in natural waters and their sources. Notes: Water is a mixture of minerals and covalent molecules.

13-TB03 Title: Table 13.3 Some Substances Added to Water Caption: A list of substances found in water from the breakdown of organic matter. Notes: The breakdown of organic matter produces ions and covalent molecules.

13-TB05 Title: Table 13.5 Drinking Water Standards Caption: Limits on water pollutants established by the EPA. Notes: Water standards are classified as primary or secondary.

13-TB06 Title: Table 13.6 Summary of Wastewater Treatments Caption: Comparison of different wastewater treatments. Notes: Wastewater treatments are classified as primary, secondary, and advanced.

13-TB07 Title: Table 13.7 Average Daily Water Use Caption: Amount of water used daily by a person for different activities. Notes: Water use may be direct or indirect.