Recreational divers typically rinse their equipment in “communal” tanks filled with fresh water after
completing dives. Often all the equipment (wetsuits, booties, fins, BCDs, regulators with mouthpieces and
masks) is rinsed in common tanks. In some facilities, a separate tank is provided for rinsing regulators.
Masks are often rinsed and even stored in a common tank on boats before a dive.
Few studies have addressed the possibility that these communal rinse tanks may harbor pathogens and
transmit disease. We first reported that communal rinse tanks at a dive facility in Roatan indeed contained
significant levels of many types of microorganisms (Microbe, December 2007, p. 577). However,
because that dive facility did not allow us to sample the water entering rinse tanks, we were unable to
determine if the microorganisms originated from the water used to fill tanks or from equipment that was
rinsed in the tanks.
Recently, a report documented the spread of conjunctivitis among divers using two dive boats off of
Fiji’s Vitu Levu Island (Undersea and Hyperbaric Medicine, 2008 vol. 35, p. 169). Among 29 divers,
14 cases (almost 50 percent) of conjunctivitis were ultimately documented. The pattern by which
conjunctivitis was spread among divers and between boats was consistent with the outbreak arising from the
divemaster, a Fijian resident, who reported having an eye infection prior to the outbreak and who placed
his own mask in the communal mask container (Undersea and Hyperbaric Medicine, 2008 vol. 35, p.
169). This study established that disease can be transmitted among scuba divers via communal tanks. (Read
our interview with the study’s author in our September 2008 issue.)
In October 2007, we investigated the extent to which bacteria were introduced into communal rinse tanks,
via water used to fill tanks and via dive equipment rinsed in them, and whether cleaning a rinse tank with
bleach once a day reduced the subsequent bacterial population. A dive facility in Bonaire cooperated in
this study but wished not to be identified.
Samples from boats returning from afternoon dives showed very high
levels of many types of bacteria.
The facility had two rinse tanks for general equipment and one tank for regulators. Each morning for
three days, at 7:30 a.m., one equipment rinse tank, designated “A” was emptied, scrubbed using undiluted
bleach, then rinsed several times and filled with fresh water from a hose. The other equipment rinse tank,
“B,” was emptied, rinsed several times with water and filled with water from the same hose but was not
bleached. We did not empty, clean or fill the regulator rinse tank. During the day, dive staff would
occasionally drain and refill equipment and regulator rinse tanks. Water samples were obtained from the
three tanks three times daily: 8 a.m., 1 p.m. and 5 p.m. The samples were placed in a refrigerator until
the day of departure, then put in a suitcase, placed in a refrigerator 12 hours later, and finally examined
for colonies and photographed. Pictures of plates can be viewed as a PowerPoint presentation at http://www.hsc.wvu.edu/som/bmp/miller.asp - - click the “Bonaire 2007” link under
the topic “Research.”
No bacterial colonies were observed from water samples filling the rinse tanks. The 8 a.m. water
samples, immediately after equipment tanks were cleaned with bleach (A) or not cleaned with bleach (B) and
filled with water, did not give rise to any colonies on all three days.
In contrast, 8 a.m. water samples in the regulator rinse tank contained a high level of bacteria on all
days tested. Presumably the regulator rinse tank had been used to rinse regulators the previous day and
after night dives. At 1 p.m. and 5 p.m., rinse tanks A, B and the regulator rinse tank usually showed high
levels of bacterial contamination. Cleaning tank A with bleach did not reduce the subsequent bacterial
level. In several instances, water samples showed low levels of bacteria -- this was apparently because the
tanks had been recently drained and refilled. It was only possible to obtain water samples from two mask
rinse tanks, both at 4 p.m., as boats were returning from afternoon dives. Both of these samples showed
very high levels of contamination by many types of bacteria.
Our studies show that bacterial contamination of divers’ rinse tanks at this Bonaire facility was
introduced by rinsing equipment, not by water used to fill tanks. Presumably, other potential pathogens,
like viruses, are also introduced into the rinse tanks. If divers with a communicable illness (like
conjunctivitis, the “common cold,” infectious mononucleosis, diphtheria and streptococcal infections) rinse
equipment in a tank, people who rinse after them may pick up the transmitting microorganism and become
infected.
We conclude that, if possible, scuba equipment, especially mouthpieces and masks, should be rinsed well
with fresh water or alcohol swabs rather than in communal tanks, to reduce the potential of spreading or
contracting disease. Studies are now in progress to identify the bacteria that inhabit the rinse tanks.
Michael R. Miller is a professor of biochemistry at West Virginia University, and
Tammy S. Miller is senior office administrator of the department of microbiology and immunology at West
Virginia University.
