Improper Backflow Prevention Could Lead to Copper Poisoning

Soda fountain machines are found in almost every establishment. Although those fizzy drinks are a tasty treat proper installation and maintenance is needed to prevent problems.

The machines work by mixing flavored syrup with carbonated water to make soda. The carbonated water is made by taking regular tap water and adding carbon dioxide (CO₂) gas creating carbonic acid. Without the carbonation fizz, it is no different than flavored syrup. When CO₂ is mixed with water, carbonic acid (a weak acid) is formed. Many water supply lines are made from copper. If CO₂ backs up into a copper water line, carbonic acid will dissolve some of the copper. 
 The water containing the dissolved copper will eventually be used in dispensing soft drinks and the first few customers receiving the drinks are likely to suffer with the symptoms of copper poisoning. Symptoms of copper poisoning by ingestion include vomiting and gastrointestinal distress.

On July 29, 1986, a woman and two girls attending a county fair in southwest Missouri came to the first aid station complaining of vomiting and abdominal distress. The symptoms occurred after consuming a carbonated beverage from a local stand, and investigation found that the soda from this stand contained elevated levels of copper and zinc. Examination of a simple check valve in one of the lines of the carbonation system revealed a stuck spring allowing backflow to occur.

On January 1, 1989, twelve children from daycare centers in the Dallas, Texas area suffered severe vomiting and stomach cramps after drinking water and soda at a movie theatre. It was discovered that a soda dispenser had malfunctioned the previous day allowing carbonated water to flow back into the water pipes of the building. This water had remained in the lines overnight and leached copper from the pipes. The next day, the copper-laced water flowed back into the soda machine and to a nearby water fountain. Later tests confirmed that the children suffered from copper poisoning.

If the proper backflow prevention device is used, the chances of copper poisoning are reduced or eliminated. The most common device, and the one required by the Kansas Food Code, is a dual check valve with an intermediate vent (American Society of Sanitary Engineering Standard #1022). The device consists of two independent check valves with an atmospheric port (vent). The port is between the check valves and will vent liquids and gases under backflow conditions. The device to be installed upstream from a carbonating device and downstream from any copper in the water supply line and to be preceded by a screen of not less than 100 mesh to 1 inch. Newer installations will most likely have the screen built into the carbonator pump.