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Technical briefs
1 Waterrncoinps
Chlorination
Method
Chlorination is one of the best methods of treating drinking water (relatively simple, effective and easy to measure) In
spite of thu relative simplicuty~it should not beforgotten that In an emergencysifuafien it is alssiys preferable to usea
groundwater source which can be protected and monitored in terms of environmental hygiene (see technical brief
Protecting a well)
Chlorination deniands staff trained In the technique and In its monitonng as well as good logistics (supply of chlorine
product. storage, etc )
In practice
Only the chlorination of a known volume of water in a reservoIr Is discussed here.
— The pnnople is to add enough chlorine-generating product to destroy all the organIc matter contained m
the water and to leave a small fraction ofchlorine available fordealing with any possible reintioduction of
organic matter To determine how much chlorine product to add, the chlorine demand Is measured
I Prepare a 1% chlorine solution (see technical brief Clslorine-goneralung products)
a Take 3 or 4 non-metallIc containers of known volame (e g 201 buckets).
3 Fill the contamers with some of the water to be treated,
4. Add to each bucket a progressively greater dose of 1% solution with a syringe.
lot container’ ImI
2nd contaIner l,Sml
3rd container 2m1
4th contaIner - 25ml
5 Wait 30 minutes (essential this Is the minimum contact time for the chlorine toreact)
6 Measure the free chlorine residual in each bucket (see technIcal brief Monitoring chlorination).
7 Choose the sample which shows a freeresidual chlorine level between 0.2 and 0.5mg/I
8 Extrapolate the 1% dose to the volume of water to be treated,
92ourthe solution into the reservoir, mix well (during filling) and wait30 minutes before distributing
Example
of water in a
—Chlorination
Foliow steps 5-5 above.
tnputa
1Several
containers of the ~e
1% solutIon
2,0001reservoir
- The
the buckets,
free residual
measi~
chlorine
hofflevels
an hour
of the
afterwater
addin~
in
1, 1 5, 2 and 2 Sm! of 1% chlorine solution
respectively are as foliowr
I 0mg/i
2 ‘0 1mg/I
3
04m
I
~
~
known volume
etC)
5m1syringe
— Measuring equipment (comparator and DPDI
/1
— The dosing rate4.ImgPl
chosen thamfore will be that for
bucket number 3 (result between 0.2 arid
05mg/i)
— If it needs 2m1 of 1% solution to chlorinate 201 of
water at the correct dosage, then it needs ~
times an much to chlorinate 2,0001, e.g.
100 x 2m1 = 200 ml of 1% chlorine solution
r
tabl~)
=
-
=
The MSF chiennat on lot available through MSF
stirs, cantains all tSe material needed for
chlorination anddosing.
Important
Never chlorinate turbid water because the suspended particles can protect miao-organisms. The
measurement of free residual chlorine may Indicate a satisfactory result (between 0,2 and 0,Smg/l), but
there Is noway of knowing if the chlorine actually comes into contact with all the pathogens. Water to be
chlorinated must contain as bttie visIble suspended material as possible If it Is turbid, apretreatment such
as sedimentation and/orfiltration shouldbe done before chlorination
— Chlorination is effective against practically all pathogenic nuao-organlsnus in water The only way to be
sure of this effectIveness Is to dose the free residual chlorine Jiuuportant even if the dosage rate is
correctly deternuned, the chlorinedemand may vary over time with unexpected changes irsthe amount of
organic material us the water. It Is thus Important to measure the free residual chlorine frequently in order
to be able to adlust the dosage rate to the situation
— Metal consumes chlorine, so never prepare strong solutions Inmetal containers (unless they are enamelled
orpainted)
— Concentrated chlorine products should be kept In a dry, shaded place, and guarded (Chlorine is
dangerous, particularly for cluldren) When in contact with are chlorine produces a corrosive and toxic gas
heavier than air The ventilation of chlorine stores should therefore be by means of vents at the bottom of
the walls
— The doses of 1% dulorine solution Øvenhere for the example of calculating chlorine demand are only an
indication, It maybe that the chlorine demand of water to be treated in the field is very different from this
—
example
— The taste of chlorine in water Is no
proof of the presence of free residual chlorine (it could be combined
residual chlorine)
-I
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