Chapter 6 WATER SUPPLY

The water supply should be ample, clean, and potable with adequate pressure and facilities for its distribution in the establishment and its protection against contamination and pollution.

1. Potable Water

An adequate supply of fresh clean water is of primary importance in plant operations. The first requirement is that the water supply to the plant be potable or safe for human consumption or food processing. The plant water supply must meet the pot ability standard s in the National Primary Drinking Water Regulations issued by the Environmental Protection Agency (EPA).

2. Back flow

Public health officials have long been concerned about cross-connections that may permit backflow in potable water supply distribution systems. Cross-connections may appear in many forms and in unsuspected places. Reversal of pressure and flow in the water system may be unpredictable. Plumbing cross- connections between a potable and non-potable water supply may constitute a serious public health hazard. There are numerous cases where cross-connections have been responsible for contamination of potable water and have resulted in the spread of disease. These concerns, as they relate to meat and poultry plants, deserve special attention. The problem is continual as potable water and piping systems are installed, repaired, replaced, or extended.

Two basic types of hazard may be created in piping systems: the solid pipe with valved connections and the submerged inlet. The solid pipe connection is often installed to supply an auxiliary piping system from the potable source. It is a direct connection of one pipe to another pipe or receptacle. Solid pip e connections may be made accidentally to waste disposal lines when it is in correctly assumed that the flow will always be in one direction. An example would be connecting a line carrying used, non-potable cooking water from a water jacket or condenser directly to a waste line without an air gap (see below). ‘‘Backflow ’’ will occur with a submerged inlet if the pressure differential is reversed without an air gap . Submerged inlets are created when the outflow end of a potable water line is covered with water or other liquid. The other liquid may not be potable. Submerged inlets could be created by a hose lying in a pool or puddle of water on the floor.

Once a cross-connection exists, any situation that causes a pressure differential with the potable line having the lower pressure can result in contamination of the entire water distribution system and potable water supply. This is called backflow and can be produced under a variety of circumstances as illustrated below:

  • Backsiphonage is one form of backflow. It is caused by negative pressure in the delivery pipes of a potable water supply and results in fluid flow in the reverse direction. It may also be caused by atmospheric pressure exerted on a pollutant liquid source that forces the pollutant in to a potable water supply system that is under vacuum. The action in this case is the common siphon phenomenon. The negative pressure differential that will begin the siphoning action is a potential occurrence in any supply line.
  • Differential pressure backflow refers to a reversed flow because of backpressure other than siphonic action. Any interconnected fluid systems in which the pressure in one exceeds the pressure of the other may cause flow from one to the other because of the differential. This type of backflow is of concern in buildings where two or more piping systems are maintained. The potable water supply is usually under pressure from the city water main.
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