The recent Centers for Disease Control’s (CDC) confirmations of a deadly brain-eating amoeba that has been found in two (2) drinking water systems in Louisiana should be a cause for concern by water system professionals.  While incidents of this nature are very rare, with only 128 cases (according to CDC) reported nationwide since 1962, it is troubling that 3 cases have been recorded in Louisiana within recent years; 2 within the same water system.  Unfortunately, each of the Louisiana cases lead to death.  It should be noted that in the vast majority of the nationwide cases, the individuals contracting the amoeba did so through non-public water supply sources.  However, there are documented cases of individuals contracting the amoeba through the public water supply system.  It is unknown how the amoeba entered the Louisiana water systems; however, let’s consider whether or not backflow could be a contributing factor.

Backflow Basics

Water always flows from high pressure to low pressure.  Backflow is generally caused by either backsiphonage (loss or decrease of water system pressure) or backpressure (an increase in the customer side pressure above supply pressure).  Backsiphonage typically occurs due to water line breaks (loss of supply pressure) or opening a fire hydrant (decrease of supply pressure).  Backpressure typically occurs when a customer increases pressure through the use of a pump to override system pressure.  In general, backflow is thought of as a loss or increase in pressure.  While the loss or increase in pressure contributes to a backflow condition, it is actually the differential pressure at the moment of pressure loss that can cause the backflow process to begin.

System Conditions

Let’s explore system conditions to determine if design and/or operations can contribute to the contamination of the very same water system we seek to protect.  Water systems consist of a water source (well or surface water plant), distribution piping complete with fittings and valves, water storage facilities, and pumps.  Each of the components of the water system should have been designed and approved by professionals to meet current standards.  Assuming construction occurred in the proper manner, the system should function as intended, and, with proper operation by trained personnel, safe water would be distributed to customers.

Backflow Scenario

Let’s create a scenario where broken water lines, pumps, and closed valves are present within the properly designed water system.  Also, let’s assume that pressure is maintained throughout the system; however, chlorine residuals are not always at acceptable levels.  What potential impact do broken water lines, pumps, closed valves, and low chlorine residuals have on the quality of water being delivered to customers?

Consider that broken water lines are immediate cross connections whereby potable water is directly connected to a non-potable source (soil on outside of piping network).  The degree of hazard increases significantly if the water line is located beneath a ditch that is receiving discharge from septic tanks or other sources.  The likelihood of contamination is very real if chlorine is not present at required levels.  However, since water will flow from high to low pressure, contamination cannot occur if sufficient pressure is maintained on the system.

Pumps are necessary to maintain pressure and distribute water throughout the system.  However, the physical operation of the pump could actually contribute to the contamination of the water system through normal operation if broken water lines are present.  When pumps begin operation, the suction side “draws” water at a higher velocity which creates an immediate differential pressure on the supply side of the pump.  Should the broken water line be located near the supply side of the pump, the differential pressure within the water line at the break can backsiphon contaminants into the water system.  In essence, the increase in velocity of the water could cause a reduction in pressure at the break and aspirate contaminants into the water system.  Under the same broken line conditions mentioned, backflow of contaminants into the system can occur on the discharge side of the pump as well.  If a valve is closed within the piping network when the pump starts, water hammer may occur.  Water hammer is defined as a pressure surge or wave caused when a fluid in motion is forced to stop or change direction suddenly.  In simpler terms, it is the recurring pressure differential (high to low) within a section of water line until the energy of the water is equalized.  If water hammer is occurring over a section of broken water line, contaminants may enter the water system  by the aspirator effect.

Conclusions

Very simply, low or non chlorinated water could be contaminated by the aspirator effect through broken water lines and distributed to customers.  It is imperative that all water system professionals evaluate the operation of water systems to minimize water hammer and repair broken water lines as breaks occur.  In addition, proper chlorination is a must if we are to continuously provide clean, safe drinking water.

 

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