Examples of Backflow Incidents

There are numerous and well documented cases where cross-connections have been responsible for contaminating drinking water resulting in the spread of disease. The problem of cross-connection control is a continual one because piping systems are constantly being installed, altered, or extended. A cross-connection may never be a problem until the right circumstance occurs resulting in backflow and an outbreak of disease.

Even in or near our own city, the right circumstances occurred resulting in cross-connections as evidenced by the following incidents. The first documented incident occurred in Huskerville, Nebraska, in 1952. Huskerville was a separate political entity, then located approximately eight miles northwest of Lincoln. Basically, this area is adjacent to and north of the area now referred to as Arnold Heights, a residential subdivision near the old Lincoln Air Base. The area, originally built as a military base hospital, was converted in 1946 to a housing area for married students attending the University of Nebraska. The area was approximately three blocks wide and five blocks long. A detailed study conducted by two research doctors within the Lincoln area revealed a very close spatial relationship between the distribution of polio cases and the location of flush valve water closets not provided with vacuum breakers. There was also a relationship between the outbreak and the occurrence of extreme fluctuations of pressure within the water mains in the area. A full report was published in the American Medical Association Journal regarding this tragedy, which left two dead and 18 persons permanently paralyzed with polio.

Also within the past several years, we have experienced back siphonage conditions resulting in milk in our distribution mains near a local creamery and hot boiler water in our distribution system near a public high school. Both of these backflows were initiated by broken water mains.


On or around this date, Lincoln Water System was called to a building for a complaint of bad tasting water. A RPZ backflow preventer was and continues to be in place on the domestic water supply and no other complaints in the area were reported. After some investigation, Lincoln Water System discovered that a new CO2 bottle had been installed on their post-mix carbonator system but was empty. There was no backflow prevention device on this machine. It was discovered that not only was one person ill, but as many as a dozen people also were sick with flu-like symptoms. An RPZ backflow preventer was installed on the post-mix carbonator and no more problems have been reported.


On June 28, 1995, the Lincoln Water System was called to the area of South 50th & "M" Streets with complaints of a lot of air in the water and milky color. After four (4) hours of flushing hydrants all over this area and no progress was being made, Lincoln Water System went to investigate possible sources. First, we checked a building at 49th & "O" Street and found nothing there. On further investigation we went to another building in this area and talked to the manager. After looking over the building, the manager said he may know the source of the problem. In the southwest corner, a water cooled compressor that the manager knew had a leak in the holding tank and was to have been shut off, but was somehow turned on. The compressor was shut off and unhooked, more flushing continued and after a short time the air was out of the main and the water back to normal.

A Lincoln Water System representative then went to this building to perform a cross-connection survey. At the time, it was determined the building would require a RPZ backflow preventer on the domestic line, right after the meter, with a RPZ on the boiler.

The building meter was in a meter pit, so it was determined that a RPZ would be installed at point of entry for the service pipe. The piping entered the building in two (2) spots, so two (2) RPZ's were installed on the building. The backflow prevention devices have been installed and no more problems have occurred.


A local college called the Lincoln Water System with "blue water" in various locations around the building (kitchen, utility room deep sink, child care area). Lincoln Water System representatives met with maintenance personnel and checked for the source of the problem. It was determined that the boiler had nothing on it but a single check (non-testable device). Samples were taken and showed sodium nitrate, a closed system water inhibitor used for boilers and closed loop systems. Reduced pressure backflow preventers were installed on the boiler lines at the same time the post-mix beverage machine was inspected and found to have no backflow device. A dual check with vent was installed on both machines with ½-inch RPZ backflow preventers to be installed later.

On January 4, 1995, "blue water" was still showing up, but not as severe. More samples were taken and showed the same chemical. At this time the maintenance personnel found a cross-connection between the chilled water system that was shut off for the winter and bypassed around the circulation pump. A single check was found as the only protection between the chilled water system and the domestic water supply to the rest of the building. A reduced pressure backflow preventer was installed on the chilled water line. The problem has not reoccurred and samples show no trace of sodium nitrate.

1994 Nebraska

While working on a chiller unit of an air conditioning system at a nursing home, a hole in the coil apparently allowed Freon to enter the circulating water and from there into the city water system.