What Causes Backflow
Public Health Significance of Cross-Connections
Public health officials have long been aware of the impact that cross-connections play as a threat to the public health. Because plumbing defects are so frequent and the opportunity for contaminants to invade the public drinking water through crossconnections are so general, enteric illnesses caused by drinking water may occur at most any location and at any time. The following documented cases of cross-connection problems illustrate and emphasize how actual crossconnections have compromised the water quality and the public health.
Human Blood in the Water System
Health Department officials
cut off the water supply to
a funeral home located in a
large southern city, after it was
determined that human blood
had contaminated the fresh
water supply. City water and
plumbing officials said that they
did not think that the blood
contamination had spread
beyond the building, however,
inspectors were sent into the
neighborhood to check for
possible contamination. The
chief plumbing inspector had
received a telephone call
advising that blood was coming
from drinking fountains within
the building. Plumbing and
county health department
inspectors went to the scene
and found evidence that the
blood had been circulating in
the water system within the
building. They immediately
ordered the building cut off
from the water system at the
meter.
Investigation revealed that
the funeral home had been
using a hydraulic aspirator to
drain fluids from the bodies of
human “remains” as part of the
embalming process. The
aspirator directly connected to
the water supply system at a
faucet outlet located on a sink
in the “preparation” (embalming)
room. Water flow through
the aspirator created suction
that was utilized to draw body
fluids through a hose and
needle attached to the suction
side of the aspirator.
The contamination of the
funeral home potable water
supply was caused by a combination
of low water pressure in
conjunction with the simultaneous
use of the aspirator.
Instead of the body fluids
flowing into the sanitary drain,
they were drawn in the opposite
direction—into the potable
water supply of the funeral
home!
Employee Health Problems due to Cross-Connection
A cross-connection incident
occurring in a modern
seven-story office building
located in a large city in New
Hampshire, in March, 1980,
resulted in numerous cases of
nausea, diarrhea, loss of time
and employee complaints as to
the poor quality of the water.
On Saturday, March 1,
1980, a large fire occurred two
blocks away from a seven-story
office building in this large
New Hampshire city. On
Sunday, March 2, 1980, the
maintenance crew of the office
building arrived to perform the
weekly cleaning, and after
drinking the water from the
drinking fountains, and
sampling the coffee from the
coffee machines, noticed that
the water smelled rubbery and
had a strong bitter taste. Upon
notifying the Manchester Water
Company, water samples were
taken and preliminary analysis
disclosed that the contaminants
found were not the typical
contaminants associated with
fire line disturbances. Investigating
teams suspected that
either the nearby fire could
have siphoned contaminants
from adjacent buildings into the
water mains, or the contamination
could have been caused by
a plumbing deficiency occurring
within the seven story building
itself.Water ph levels of the
building water indicated that
an injection of chemicals had
probably taken place within the
seven-story building. Tracing of
the water lines within the
building pinpointed a 10,000
gallon hot-water storage tank
that was used for heat storage
in the solar heating system. It
did not have any backflow
protection on the make-up supply line! As the storage tank
pressure increased above the
supply pressure, as a result of
thermal expansion, the potential
for backpressure backflow
was present. Normally, this
would not occur because a
boost pump in the supply line
would keep the supply pressure
to the storage tank always
greater than the highest tank
pressure. The addition of rust
inhibiting chemicals to this
tank greatly increased the
degree of hazard of the liquid.
Unfortunately, at the same time
that the fire took place, the
pressure in the water mains was
reduced to a dangerously low
pressure and the low pressure
cutoff switches simultaneously
shut off the storage tank
booster pumps. This combination
allowed the boiler water,
together with its chemical
contaminants, the opportunity
to enter the potable water
supply within the building.
When normal pressure was
reestablished in the water
mains, the booster pumps
kicked in, and the contaminated
water was delivered
throughout the building.