Why Backflow Occurs 1
What would cause the water pressure in a public water distribution system or domestic water plumbing system to change?
A demand in water that is greater than the public water system capacity, reduces the pressure in the domestic internal piping system. Examples of such demands are listed below:
- Water Main Break
- Fire Fighting
- Hydrant Flushing
- Pump Repair
- Service Shut-off
- Valve Exercising and Repair
- High Water Demand
- Inadequate Water System Pressures
Some of the incidences listed are predictable but others are not easily foreseen and can occur at any time. Whether the incidences are predictable or not, the incidences when they occur will cause the pressure in the potable water system to change and reverse the direction of flow.
What happens to the public water system pressure when a water main breaks? Since water flows from high pressure to low pressure, the water in the public water distribution system is flowing towards the water main break. A pressure differential has been created within the public water distribution system. The pressure in the area of the water main break is atmospheric. The water main break reduces the pressure in the domestic internal water system to below atmospheric pressure and a backsiphonage situation is occurring within the building domestic internal plumbing system. Anyone drinking water within the premises of a building near the water main break may be consuming water that is non-potable if there are unprotected cross-connections within the building domestic plumbing system. Water main breaks are unpredictable for the most part. That is why it is important to control cross-connection where they exist. If they are not controlled at all locations, the consumers are at risk when there is a water main break.