CDC 6 (175) DTZS 
© TBS 2021                                                                                                Second Edition 2021  
 
 
DRAFT TANZANIA STANDARD 
  
  
 
 
 
 
 
 
 
 
 
 
 
 
Sodium hypochlorite used for disinfection of water intended for 
human consumption – Specification  
  
  
  
  
  
  
  
  
  
  
  
 
 
 
 
 
 
 
 
 
 
 
TANZANIA BUREAU OF STANDARDS 
 
   
  
   
 
 CDC 6 (175) DTZS 
 
© TBS 2021                                                                                                Second Edition 2021 
    
 Foreword  
  
This Draft Tanzania Standard is being developed by the Water Quality Technical Committee under 
supervision of the Chemical Division Standards Committee and it is in accordance with the procedures of 
the Bureau. 
  
In the preparation of this Tanzania Standard assistance has been drawn from:  
  
  
ANSI /AWWA B 300: 1980, Standard for hypochlorite, published by the American  
National Standards Institute/American Water Works Association.   
  
 
BS EN 901: 1999, Chemicals used for treatment of water intended for human  
consumption – Sodium hypochlorite, published by European Community. 
  
SANS 50901:1999 Chemicals used for treatment of water intended for human 
consumption — Sodium hypochlorite published by South African National 
Standard. 
 
IS 11673 Sodium Hypochlorite Solution — Specification Part 1 Household and 
Industrial Use  published by Bureau of Indian Standard (BSI). 
  
In reporting the result of a test or analysis made in accordance with this Tanzania 
Standard, if the final value observed or calculated, is to be rounded off, it shall be 
done in accordance with TZS 4 (see clause 2).  
  
 
 
 
   CDC 6 (175) DTZS 
© TBS 2021                                                                                                Second Edition 2021  
  
 
DRAFT TANZANIA STANDARD                                            CDC 6 (175)  DTZS 
 
Sodium hypochlorite used for disinfection of water intended for 
human consumption –– Specification  
 
 
1 Scope   
  
This Draft Tanzania Standard specifies requirements, sampling and test methods for sodium hypochlorite 
solution used in disinfection of water intended for human consumption.  
  
2   Normative references   
  
The following referenced documents are indispensable for the application of this document. The latest 
edition of the referenced document (including any amendments) applies; 
  
TZS 59 /ISO 3696 Water for analytical laboratory use – Specifications and test methods   
  
TZS 4 Rounding off numerical values   
  
3 Terms and definitions 
3.1. water intended for human consumption 
all water either in its original state or after treatment, intended for drinking, cooking, food preparation or 
other domestic purposes, regardless of its origin and whether it is supplied from a distribution network, 
from a tanker, or in bottles or containers 
 
4    Requirements   
  
4.1 General requirements 
 
4.1.1 Descriptions  
  
     4.1.1.1 Chemical name; Sodium hypochlorite  
 
     4.1.1.2 Relative molecular mass; 74.44  
  
     4.1.1.3 Empirical formula;  NaOCI 
                           
     4.1.1.4 Chemical formula; NaCIO  or NaOCI  
  
 
4.1.2 Physical properties   
    
4.1.2.1 Sodium hypochlorite solution shall be a clear, slightly yellow or slightly cloudy liquid and shall be 
miscible in all proportions with water.   
  
4.1.2.2 Sodium hypochlorite solutions shall contain no soluble mineral or organic substances in a quantity 
that would be deleterious or injurious to anyone consuming water disinfected with acceptable quantities of 
the hypochlorite.  
 
4.2 Specific requirements 
The material, when tested according to the methods prescribed in Annexes A, B, and C shall comply with 
the specific requirements given in Table 1.  
 CDC 6 (175) DTZS 
 
© TBS 2021                                                                                                Second Edition 2021 
 Table 1 Specific requirements for Sodium hypochlorite. 
 
S/N Characteristic Requirement  Method of test  
i. Available chlorine content,  
% wt /volume  0.5 - 1.0  annex A 
ii. Total free alkali (as NaOH)  
% weight by volume, max 1.2 annex B 
 
iii. Insoluble matter,%  ( max) 0.15 annex C  
iv. Iron (as Fe), ppm, max.  0.4  Annex D  
v. Neat pH range  9 - 12  
  
  
5 Packaging and Marking  
  
5.1  Packing     
Sodium hypochlorite shall be packed in a suitable airtight container that prevents it from deterioration of 
its quality during storage, transportation and handling.  
  
5.2  Marking  
  
The following information shall be legibly and indelibly marked on the container.  
  
a) name and formula of product, 'SODIUM HYPOCHLORITE'(NaOCI).   
b) name and address of the manufacturer. 
c) the net volume of the contents.  
d) the batch or code number.  
e) the nominal available chlorine content.  
f) dates of manufacture and best before. 
g) the instruction for use and handling.   
h) first aid instructions. 
i) the words 'STORE IN A COOL DRY PLACE AWAY FROM DIRECT SUNLIGHT '. 
j) hazard warning in symbol or words. 
   
      
6 Sampling   
Sampling for Sodium hypochlorite shall be done as per Annex E. 
  
7 Testing   
Methods of test for Sodium hypochlorite shall be as prescribed in the annexes.  
  
 
  
 
 
 
 
 
 
 
 
 CDC 6 (175) DTZS 
© TBS 2021                                                                                                Second Edition 2021 Annex A  
(normative)  
Method of determination of available chlorine content  
 
A.1   Summary of method   
 
The sample is added to an acidified solution of potassium iodide and the released iodine is titrated with 
standard sodium thiosulphate solution to the usual starch end point.   
  
A.2 Reagents   
  
A.2.1 Acetic acid, glacial.  
  
A.2.2 Potassium iodide (KI), crystals, iodate free.  
  
A.2.3 Sodium thiosulphate (Na 2S2O35H20), Standard solution (0.1N).  
  
Dissolve 25 g of Na 2SO3 crystals in freshly boiled and cooled water and dilute to 1 L. The solution is more 
stable if the glass ware is cleaned with sulphuric-chromic acid and thoroughly rinsed with water.  
Standardize against potassium iodate (KIO 3) as follows: Weigh out accurately 3.567 g of dry KIO 3 and 
transfer to a 1 L volumetric flask.  Dissolve with water, make up to the mark and mix thoroughly.  This 
solution will be exactly 0.1000 N. To standardize the Na 2SO3 solution, carefully pipette a 50 mL aliquot of 
the KIO 3 solution into a 250 mL Erlenmeyer flask and dilute to 100 mL with water. Add 1 g of KI crystals.  
When it is dissolved, add 15 mL of 1.0 N hydrochloric acid and titrate immediately with the Na 2S2O3 
solution.  When the solution becomes light yellow, add 1 mL of starch indicator solution and complete the 
titration to the disappearance of the blue colour. Standardize at least monthly.  Calculate the normality of 
the Na 2S2O3 solution as follows:  
  
   
Normality, N 1 =ହ଴ ×଴.ଵ
஺      
 
      where,  
  
      A is the value of Na 2S2O3 solution required for titration of KIO 3 solution, mL.    
                            N 1 is normality of the Na 2S2O3 
      
A.2.4 Mix 0.5 g of soluble starch with 5 mL of cold water and add to 95 mL of boiling water. Mix, cool and 
store in a sterilized bottle.  Replace frequently or add 0.1% salicylic acid to minimize deterioration.  
  
A.3 Procedure  
  
Dissolve 2 to 3 g of KI crystals to 50 mL of water in a 250 mL Erlenmeyer flask.  Add 10 ml of acetic acid.  
Then pipette the aliquot of sample into the solution keeping the tip of the pipette beneath the surface of 
the solution until drained. Titrate at once with 0.1 N Na2S2O3 solution until the iodine colour is nearly gone 
then add 1 mL of starch indicator solution and complete the titration to the disappearance of the blue 
colour.  Record the titration as A.  
  
A.4 Calculations  
  
A.4.1 Calculate the available chlorine, percent mass by volume as follows:   
    
     available chlorine as Cl,% g/L =(஺ேభ ௑ ଷହ.ସ଺)୶ ଵ଴଴  
௏ 
              
  
  
 
A.4.2 Calculate the sodium hypochlorite content, percent mass by volume as follows:  
  CDC 6 (175) DTZS 
 
© TBS 2021                                                                                                Second Edition 2021 
                                                             
Sodium hypochlorite (NaOCl),% g/L =(஺ேభ ୶ ଷ଻.ଶଶ)୶ ଵ଴଴ 
௏     
                
              where,  
  
A   is the volume of Na 2S2O3 solutionrequired for titration of the sample, mL;  
  
N1  is the normality of the Na 2S2O3  solution; and  
  
V   is the volume of original sample in aliquot used, mL.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 CDC 6 (175) DTZS 
© TBS 2021                                                                                                Second Edition 2021 Annex B  
(normative)   
Method of determination of sodium hydroxide content  
  
B.1 Summary of method    
  
A sample is added to a neutralised, mixed solution of barium chloride and hydrogen peroxide, which 
precipitates any carbonate and reduces the hypochlorite to chloride.  The free alkali is then titrated with 
standard hydrochloric acid using phenolphthalein indicator.  
  
B.2 Reagents  
  
B.2.1 Barium chloride solution (100 g/L)   
  
Dissolve 100 g of chemically pure barium chloride (BaCI 2.2H2O) in distilled water and dilute to 1 L with 
distilled water.  Filter the solution if turbid.  
  
B.2.2 Hydrochloric acid, standard (0.1 N)  
  
Prepare a 0.1 N solution of hydrochloric acid (HCI) and standardize against primary standard solution 
carbonate and methyl red mixed indicator.  
  
B.2.3 Hydrogen peroxide, approximately 3%.  
  
B.2.4 Phenolphthalein indicator solution (0.5 g/100 mL)  
  
Dissolve 0.5 g of phenolphthalein in 60 ml of 95% ethyl alcohol and dilute to 100 L; with water.   
  
B.2.5 Sodium hydroxide solution    
  
Dissolve 4.0 g of chemically pure sodium hydroxide in distilled water and dilute to 1 L with distilled water.  
  
B.3 Procedure  
  
Place 50 mL of barium chloride solution and 30 mL of hydrogen peroxide in a 250 mL Erlenmayer flask 
(or 6.in porcelain dish), add 10 drops of phenolphthalein indicator solution and neutralize with sodium 
hydroxide solution.  Introduce into this neutral mixture 10 mL of the liquid sample, shake or stir vigorously 
for 1 min and titrate the sodium hydroxide solution with 0.1 N hydrochloric acid until the pink colour 
disappears.  
  
B.4 Calculation   
  
Calculate the free alkali as NaOH as follows:   
  
Free alkali as NaOH, g/L =௅ேమ ୶ ସ଴ 
௏ 
        
                      where    
    L    is the volume of hydrochloric acid solution used in the titration, mL;  
  
    N2    is the normality of the hydrochloric acid solution; and  
  
    V      is the volume of original sample used, mL  
 
 
 
 
 CDC 6 (175) DTZS 
 
© TBS 2021                                                                                                Second Edition 2021 
 Annex C  
(normative)  
Method for determination of insoluble matter   
 
C.1 Apparatus   
  
C.1.1 Sintered crucible    
  
C.1.2 Analytical Balance  
  
C.1.3 Oven   
  
C.2 Procedure   
  
Pour approximately 100 mL of the sodium hypochlorite solution into a tared 400 mL beaker placed on a 
laboratory platform balance and weigh to the nearest 0.1 g.  Add 100 mL of distilled water (as per TZS 
59),  and mix thoroughly.  Filter through a tared dry Sintered crucible.  Wash the beaker and crucible with 
distilled water.  Dry the crucible to a constant weight at 100-105°C.  
  
C.3 Calculation   
  
                                                  
  
Percent insoluble matter  =ୋ୰ୟ୫ୱ ୭୤ ୰ୣୱ୧ୢ୳ୣ 
ୋ୰ୟ୫ୱ ୭୤ ୱୟ୫୮୪ୣ 𝑋 100 
  
  
  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 CDC 6 (175) DTZS 
© TBS 2021                                                                                                Second Edition 2021  
  
Annex D 
(Normative) 
Determination of Iron 
 
 
 
F.1 Apparatus.  
F.1.1 Nessler Cylinders  — 50 ml capacity. 
F.2 REAGENTS  
F.2.1 Ammonium Persulphate  
F.2.2 Butanolic Potassium Thiocyanate Solution  
Dissolve 10 g of potassium thiocyanate in 10 ml of water. Add sufficient n- butanol to make up to 100 ml 
and shake vigorously till the solution is clear. 
F.2.3 Standard Iron Solution A  
Dissolve 0.702 2 g of ferrous ammonium sulphate  
[FeSO 4·(NH4)2 SO4·6H2O] in 100 ml of water (as per  TZS 59) , add 5 ml of 1: 5 ( v/v) sulphuric acid and add 
dilute solution of potassium permanganate (0.2 percent, m/v) drop wise until a slight pink coloration 
remains after stirring. Dilute with water to 1 000 ml and mix thoroughly. One millilitre of this solution 
contains 0.1 mg of iron as Fe. 
F.2.4 Standard Iron Solution B  
Take 100 ml of the standard iron Solution A ( see F-2.3) and dilute to 1 000 ml with water in a 1 000 ml 
volumetric flask. This dilute solution should be prepared fresh. One millilitre of this solution contains 0.01 
mg of iron (as Fe). 
F.3 PROCEDURE  
F.3.1  
Weigh 50.0 g of the material in a silica dish (capacity – 200 ml) and evaporate it almost to dryness over 
water bath. Dissolve the dry mass in 30 ml water, transfer quantitatively in a nessler cylinder of 50 ml 
capacity, add about 30 mg of ammonium persulphate and 15 ml of butanolic potassium thiocyanate 
solution. Make up to 50 ml, shake vigorously for about 30 s and allow the layers to separate. Carry out a 
control test in another Nessler cylinder using 2 ml of standard iron Solution B ( see F-2.4). Compare the 
intensity of the colour produced in the butanol layers in the two cylinders. 
F-3.2 The limit prescribed in Table 1 shall be  taken as not having been exceeded if the intensity of colour 
produced with the material is not greater than that produced in the control test. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 CDC 6 (175) DTZS 
 
© TBS 2021                                                                                                Second Edition 2021 
 Annex E 
(Normative) 
Sampling   
 
D.1   The following sampling procedure shall be applied in determining whether a lot, submitted for 
inspection and test, complies with the relevant requirements of the specification.   
  
D.2 Sampling from tankers  
  
Take from four levels in the tanker or at four stages during filling of the tanker a composite sample of 500 
mL.  Divide this sample into two equal portions and place each portion in a sample bottle.  Use one 
portion for the determination of the insoluble matter the available chlorine and the free sodium hydroxide 
contents.  
  
D.3 Sampling from other containers   
  
D.4 Containers with a capacity of more than 1 L.   
  
From the lot, take at random the number of containers relative to the lot size as given in table 1. From 
each container so drawn take a sample 500 mL.  Divide each sample into two equal portions and place 
each portion in a sample bottle.  Use one portion of each sample for the determination of the available 
chlorine and the free sodium hydroxide contents and reserve the other portion for the determination of the 
sodium chlorate content.  
  
D.5 Containers with a capacity of 1 L or less  
  
From the lot, take at random the number of containers relative to the lot size as given in table 1. If the 
containers are packed in cartons, take at random the number of cartons relative to the lot size and from 
each carton so drawn take at random one container. Use half of the samples for the determination of the 
insoluble matter, available chlorine and the free sodium hydroxide contents.  
  
D.6 The containers and the samples so taken shall be deemed to represent the lot.  
  
D.7 Compliance with the specification  
  
The lot shall be deemed to comply with requirements of the specification, if after sampling of the 
containers and testing of the samples taken in accordance with D.2, no defective is found.  
  
  
Table 1 – Number of containers to be taken for sampling various lot sizes  
  
  
Lot size number of containers   
Sample size number of 
containers   
  
  
1 to 4  
5 to 50  
51 to 100  
101 to 500  
501 to 1500  
1501 and above   
    
All  
4  
5  
8  
10  
12  
 
  CDC 6 (175) DTZS 
© TBS 2021                                                                                                Second Edition 2021