Element | Remarks |
Temperature | Probably the most important factor; longer survival at lower temperatures; freezing kills bacteria and protozoan parasites, but prolongs virus survival. |
Moisture | Low moisture content in soil can reduce bacterial populations. |
Light | UV in sunlight is harmful. |
pH | Most are stable at pH values of natural waters. Enteric bacteria are less stable at pH > 9 and pH < 6. |
Salts | Some viruses are protected against heat inactivation by the presence of certain cations. |
Organic matter | The presence of sewage usually results in longer survival. |
Suspended solids or sediments | Association with solids prolongs survival of enteric bacteria and virus. |
Biological factors | Native microflora is usually antagonistic. |