-7-
is more turbid (>30 units of turbidity), it can be filtered and/or decanted and then
disinfected with a double dose of sodium hypochlorite. However, it is absolutely
necessary to verify that residual chlorine remains in the water 30 minutes after
disinfection (see chapter 10).
If it is not possible to use a turbidity meter, we suggest an alternate, though
imprecise, method to measure turbidity.
To determine whether the water can be
used to produce sodium hypochlorite or
to chlorinate drinking water, fill a water
bottle to the height of this manual when
it is open and in a vertical position.
1
.
Then place the bottle over the WATA logo
and look at it from above through the
bottle.
2
. If you can read the WATA logo
through the water, this means the water
measures less than 5 units of turbidity.
W There should be ample illumination but the light should not be blinding.
The bottle should be transparent, colourless, clear and without
scratches or dirt. A flat-bottomed bottle is preferable. Since it is not
always possible to meet all of these conditions, catching a slight glimpse
of the WATA logo is acceptable.
1 2
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