Environmental Engineering Reference
In-Depth Information
that water technology has to offer for municipal systems, it is not infallible.
For municipal water filtration facilities to work properly, they must be prop-
erly constructed, operated, and maintained.
Whenever possible, persons outdoors should carry drinking water of
known purity with them. When this is not practical—when water from
streams, lakes, ponds, and other outdoor sources must be used—time should
be taken to properly disinfect the water before drinking it.
Boiling water is one of the simplest and most effective ways to purify
water. Boiling for one minute is adequate to kill
Giardia
as well as most other
bacterial or viral pathogens likely to be acquired from drinking polluted
water. Disinfecting water with chlorine or iodine is considered less reliable
than boiling for killing
Giardia
; however, we recognize that boiling drink-
ing water is not practical under many circumstances. When boiling drink-
ing water is not possible, chemical disinfectants such as iodine or chlorine
should be used. They offer some protection against
Giardia
and destroy most
bacteria and viruses that cause illness. Iodine or chlorine concentrations of
8 mg/L (8 ppm) with a minimum contact time of 30 minutes are recom-
mended. If the water is cold (less that 10°C or 50°F), a minimum contact time
of 60 minutes is recommended. If a choice of disinfectants is available, use
iodine. The disinfectant activity of iodine is less likely than that of chlorine
to be reduced by unfavorable water conditions, such as dissolved organic
material in the water or a high pH.
Table 6.5
gives instructions for disinfecting water using household tinc-
ture of iodine, and
Table 6.6
gives instructions for using chlorine bleach. If
water is visibly dirty, it should first be strained through a clean cloth into a
container to remove any sediment or floating matter. The water should then
be treated with chemicals as shown in the tables.
Portable filter devices for field or individual use as well as some house-
hold filters are available for use against waterborne giardiasis. Manufacturer
data accompanying these filters indicate that some can remove particles the
size of a
Giardia
cyst or smaller and may be capable of providing a source of
safe drinking water for an individual or family during a waterborne out-
break. If carefully selected, such devices might also be useful in preventing
TAble 6.5
2% Tincture of Iodine
Tincture of iodine from the medicine chest or first aid kit can be used to treat
water. Mix thoroughly by stirring or shaking water in the container and let
stand for 30 minutes. Very turbid or very cold water may require prolonged
contact time; let stand up to several hours or overnight.
Number of Drops (0.05 mL) per Quart/Liter
2% Tincture of Iodine
Clear Water
Cold or Cloudy Water
Number of drops per quart
5
10
