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 NAVSHIPS 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 considered in addition to the routine weekly samples for record purposes. The steps for obtaining water samples are as follows:
1. 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 laboratory.
2. Let the water run for 2 to 3 minutes.
3. Collect sample. Take care not to contaminate the cap or top of the bottle.
4. 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 during transportation.
NOTE: DO NOT TAKE SAMPLES FROM LEAKING SPIGOTS.
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 present in the water onto a thin membrane. The membrane is placed in a small petri dish containing 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 sample.
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 warranted. If no bacterial growth is noted, no action is required.
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 discrepancies 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 membrane filter analysis for coliform bacteria.