1 Scope and field of application<br>2 General<br>3 Causes of water contamination<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;3.1 Backflow<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;3.2 Cross-connection<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;3.3 Other influencing factors<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;3.4 Materials<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;3.5 Stagnation<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;3.6 Damage to the system due to lack, or lack of <br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;proper, maintenance<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;3.7 Improper operation<br>4 Backflow prevention<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.1 Single-unit and multiple-unit backflow <br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;prevention devices<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.2 Types of safety devices to be used<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.3 Typical applications of safety devices<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.4 Backflow protection of water heaters<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.5 Criteria for the selection of safety devices<br>5 Protection of drinking water in water heaters<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;5.1 Types of water heaters<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;5.2 Use of chlorinated fluorocarbons as heating <br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;medium