residual is read directly from amounts printed on
the kit next to the color standards.
Calcium hypochlorite 65 to 70 percent (HTH)
in 6-ounce plastic bottles is the only form of
chlorine that may be carried aboard ships for
disinfecting potable water.
Extreme caution must be observed in storing
and handling calcium hypochlorite. Although this
chemical itself is not combustible, it is a strong
oxidizing agent and will react readily with organic
materials such as paint, oil, solvents, and even wet
garbage. In contact with these materials, calcium
hypochlorite will produce large amounts of heat
or fire and chlorine gas. Specific handling and
storage precautions are contained in the NAV-
SHIPS Technical Manual, chapter 670.
In addition to being responsible for FAC
determinations, the MDR is required to test the
water at least weekly for bacterial content.
Bacteriological examinations should be carried
out on samples collected from the tanks and at
representative points throughout the ships
distribution system. The number of samples
should be based on the size of the distribution
system, but no less than four samples should be
tested each week. Daily samples are collected
following unsatisfactory results and are to be con-
sidered in addition to the routine weekly samples
for record purposes. The steps for obtaining water
samples are as follows:
Take chlorine reading with a calorimeter.
Record in the ships water log; if the sample
is not tested aboard the ship, prepare a DD
686 to accompany the sample to the testing
Let the water run for 2 to 3 minutes.
Collect sample. Take care not to con-
taminate the cap or top of the bottle.
Replace the cap. The sample is marked for
identification and refrigerated if it is not
to be tested immediately. If the sample is
sent off the ship for testing, refrigerate it
NOTE: DO NOT TAKE SAMPLES FROM
There are currently two acceptable methods
for testing the bacteriological quality of water.
One is the multiple-tube fermentation procedure,
which requires much laboratory preparation,
physical space, and time. The other method is the
membrane filter technique, which is the method
of choice for bacteriological testing aboard ship.
The membrane filter method uses the concept of
filtering the water sample to trap any bacteria pre-
sent in the water onto a thin membrane. The
membrane is placed in a small petri dish contain-
ing a broth media, and the plate is then incubated
for 24 hours at 35°C to see if bacterial colonies
appear. Each bacterial colony that appears
represents one bacterial cell present in the water
If bacteriological testing reveals colonies with
a greenishgold metallic sheen (coliform bacteria),
fecal contamination of the water is indicated and
the MDR must immediately institute corrective
action in accordance with the Manual of Naval
Preventive Medicine, chapter 6. If growth occurs
but none of the colonies have the characteristic
coloring, these colonies should be reported in the
water log as background colonies. Occasionally
coliforms will not produce a metallic sheen;
therefore, if consistent high counts of colonies
without the metallic sheen are obtained, further
examination of these background colonies is war-
ranted. If no bacterial growth is noted, no action
Ice intended for use in food or drink must be
manufactured from potable water only and must
be afforded the same sanitary considerations as
other foods. Ice-making machines should be
cleaned and inspected periodically by maintenance
personnel to ensure proper operation. The MDR
should be familiar with the operation of ice
machines so that design and installation discrepan-
cies that could lead to ice contamination will be
recognized. For example, ice machine drain pipes
should not be connected directly to a ships drain
line; there should be a space (air gap) between the
machine drain pipe and the ships receiving drain.
The Medical Department representative
should include ice samples in weekly
bacteriological analyses. This is accomplished by
collecting ice in sterile containers, allowing the ice
to melt, and then submitting the sample for mem-
brane filter analysis for coliform bacteria.