ICS 71.100.80  
 
Reference number  
DRS 353 -8:2023  
© RSB 2023  
  
 RWANDA 
STANDARD  DRS 
353-8  
 
3rd edition  
2023 -mm-dd 
 
Water quality  — Chemical used for 
treatment of water intended for human 
consumption  — 
8: Sodium hypochrolite  
   
DRS 353 -8: 2023  
©RSB 2023  - All rights reserved                  ii 
 In order to match with technological development and to keep continuous progress in industries, 
standards are subject to periodic review. Users shall ascertain that they are in possession of the latest 
edition  
 
 
 
 
 
 
 
 
© RSB 2023  
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized 
in any form or by any means, electronic or mechanical, including photocopying and microfilm, without 
prior written permission from R SB. 
Requests for permission to reproduce this document should be addressed to : 
Rwanda Standards  Board  
P.O Box 7099 Kigali -Rwanda  
KK 15 Rd, 49  
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Toll Free: 3250  
E-mail: info@rsb.gov.rw  
Website: www.rsb.gov.rw  
ePortal: www.portal.rsb.gov.rw   DRS 353 -8- 2023  
iii                ©RSB 2023  - All rights reserved  
 Contents  Page 
Foreword  ................................ ................................ ................................ ................................ ....................  v 
RS 127 -1:2018: Bleaching agents — Specification — Part 1:Sodium hypochlorite solutions for 
water treatment  ................................ ................................ ................................ .............................  v 
1 Scope  ................................ ................................ ................................ ................................ .............  1 
2 Normative references  ................................ ................................ ................................ ...................  1 
3 Terms and definitions  ................................ ................................ ................................ ............................  1 
4 Description  ................................ ................................ ................................ ................................ .... 1 
4.1 Identification  ................................ ................................ ................................ ................................ ........  1 
4.1.1  Chemical name  ................................ ................................ ................................ .............................  1 
4.1.2  Synonym or common names  ................................ ................................ ................................ ...... 1 
4.1.3 Relative molecular mass  ................................ ................................ ................................ .................  1 
4.1.4 Empirical formula  ................................ ................................ ................................ .............................  1 
4.1.5 Chemical formula  ................................ ................................ ................................ .............................  1 
4.2 Commercial form  ................................ ................................ ................................ ................................ . 2 
4.3 Physical properties  ................................ ................................ ................................ .............................  2 
4.3.1 Appearance and odour  ................................ ................................ ................................ ....................  2 
4.3.2 Density  ................................ ................................ ................................ ................................ ...............  2 
5 Requirements  ................................ ................................ ................................ ................................  2 
6 Packaging and labelling ................................ ................................ ................................ .........................  3 
6.1 Packaging  ................................ ................................ ................................ ................................ .............  3 
6.2 Labelling  ................................ ................................ ................................ ................................ ...............  3 
Annex  A (normative)  Testing for insoluble matter in sodium hypochlorite solution  ........................  4 
A.1 Procedure  ................................ ................................ ................................ ................................ ...... 4 
A.2 Calculation  ................................ ................................ ................................ ................................ .... 4 
Annex  B (normative)  Determination of available chlorine  ................................ ................................ ... 5 
B.1 Principle of test methods  ................................ ................................ ................................ ...................  5 
B.2 Reagents  ................................ ................................ ................................ ................................ ..............  5 
B.2.1 Glacial acetic acid  ................................ ................................ ................................ ............................  5 
B.2.2 Standard potassium iodate solution — 0.1 N  ................................ ................................ ...............  5 
B.2.4 Potassium iodine crystals — Iodate Free.  ................................ ................................ ....................  5 
B.2.5 Standard Sodium Thiosulphate Solution — 0.1 N.  ................................ ................................ ....... 5 
B.3 Procedure  ................................ ................................ ................................ ................................ ............  5 
B.4 Calculation  ................................ ................................ ................................ ................................ ...........  6 
Annex  C (normative)  Determination of free alkali  ................................ ................................ .................  7 
C.1 Principle of test method  ................................ ................................ ................................ .....................  7 
C.2 Reagents  ................................ ................................ ................................ ................................ ..............  7 
C.3 Procedure  ................................ ................................ ................................ ................................ ............  7 
C.4 Calculation  ................................ ................................ ................................ ................................ ...........  7 
Annex  D (normative)  Determination of heavy metals (as Fe)  ................................ ..............................  8 
D.1 Apparatus  ................................ ................................ ................................ ................................ ............  8 
D.2 Reagents  ................................ ................................ ................................ ................................ ..............  8 
D.3 Procedure  ................................ ................................ ................................ ................................ ............  8 DRS 353 -8: 2023  
©RSB 2023  - All rights reserved                  iv 
 Annex  E (normative)  Measurement of pH value  ................................ ................................ ...................  9 
Annex  F (normative)  Determination of sodium chlorite  ................................ ................................ .... 10 
F.1 Principle of method  ................................ ................................ ................................ ..........................  10 
F.2 Apparatus  ................................ ................................ ................................ ................................ ..........  10 
F.3 Reagents  ................................ ................................ ................................ ................................ ............  10 
F.3.1  Concentrated hydrochloric acid.  ................................ ................................ ................................  10 
F.3.2  Sodium bromide solution — 10 % w/v.  ................................ ................................ ......................  10 
F.3.3  Potassium iodine solution — 10 w/v.  ................................ ................................ .........................  10 
F.3.4  Standard sodium thiosulphate solution — 0.05 N.  ................................ ................................ ... 10 
F.3.5  Starch indicator solution — 0.5 % m/v.  ................................ ................................ ......................  10 
F.3.6  Sodium bicarbonate.  ................................ ................................ ................................ ....................  10 
F.3.7  Procedure  ................................ ................................ ................................ ................................ ...... 10 
F.4 Calculate  ................................ ................................ ................................ ................................ ............  11 
F.5 Principle of method used  ................................ ................................ ................................ .................  11 
 DRS 353 -8- 2023  
v                ©RSB 2023  - All rights reserved  
 Foreword  
Rwanda Standard s are prepared  by Technical Committees and approved by Rwanda Standards Board (RSB) 
Board  of Directors in  accordance with the procedures of RSB, in compliance with Annex 3 of the WTO/TBT 
agreement on the preparation, adoption and application of standards.  
The main task of technical committees is to prepare national standards.  Final Draft Rwanda S tandards adopted 
by Technical committ ees are ratified  by me mbers of RSB Board of Director s for publication and gazettment as 
Rwanda Standards.  
DRS 353-8 was prepared by Technical Committee RSB/TC013, Water and sanitation  
In the preparation of this standard, reference was made to the following standard  (): 
RS 127 -1:2018 : Bleaching agents — Specification — Part 1:Sodium hypochlorite 
solutions for water treatment  
The assistance de rived from the above source is hereby acknowledged with thanks.  
This third edition  cancels and replaces the second edition (RS  127-1: 2018), which has been technically revised.  
DRS 353 consists of the following parts, under the general title Water quality  —Chemical used for treatment of 
water intended for human consumption : 
⎯ Part 1: Aluminium sulphate  
⎯ Part 2: Calcium hypochlorite  
⎯ Part 3: Sodium chlorite  
⎯ Part 4: Sodium chloride  
⎯ Part 5: Bentonite  
⎯ Part 6: Hydrated lime  
⎯ Part 7: Polyaluminium chloride hydroxide and polyaluminium chloride hydroxide sulfate sodium chloride  
⎯ Part 8: Sodium hypochlorite  
 
 
 
 DRS 353 -8: 2023  
©RSB 2023  - All rights reserved                  vi 
  
 
 
 
Committee membership  
The following organizations were represented on the Technical Committee on Water and sanitation  (RSB/TC 
013) in the preparation of this standard.  
Kigali Water (METITO)  
Ruliba Clays  
Rwanda Environmental Management Authority (REMA)  
IPRC Gishari   
Rwanda Utility Regulatory Authority (RURA)  
Rwanda Water Resources Board (RWB)  
Water and Sanitation Corporation (WASAC)  
Kigali City  
P-TECHNIKS Ltd  
Development Bank of Rwanda  (BRD)  
Rwanda Standards Board (RSB) – Secretariat  
  DRS 353 -8- 2023  
vii                ©RSB 2023  - All rights reserved  
 Introduction   
Chemicals used during treatment of water have to be of good quality and meet standards requirement, in order 
to avoid any contamination of water by impurities of these chemicals and therefore ensure a successful water 
treatment.  
 DRS 353 -8: 2023  
1                ©RSB 2023  - All rights reserved  
 Water quality  — Chemical used for treatment of water intended for 
human consumption — 8: Sodium hypochlorite   
1 Scope   
This Rwanda Standard specifies the requirements and test methods for sodium hypochlorite solutions used for  
disinfection  and oxidation of  water intended for human consumption.   
2 Normative references   
There are no normative reference for this document  
3 Terms and definitions   
No terms and definitions are used in this document  
4 Description  
4.1 Identification  
4.1.1  Chemical name  
Sodium hypochlorite  
4.1.2  Synonym or common names  
Liquid bleach, soda bleach, bleach lye.  
4.1.3 Relative molecular mass  
74.44  
4.1.4 Empirical formula  
NaClO  
4.1.5 Chemical formula  
NaClO   
©RSB 2023  - All rights reserved                  2 
 4.2 Commercial form   
The product is supplied as an aqueous solution with an available (active) chlorine concentration up to a mass 
fraction of 18 %.  
4.3 Physical properties  
4.3.1 Appearance and odour  
Sodium hypochlorite solution (NaClO) is a clear light -yellow liquid with a faint chlorinous odour.  
4.3.2 Density  
The density of the product varies between 1.13 g/mL and 1.30 g/mL at 20 °C  
5 Requirements  
5.1 Sodium hypochlorite solution shall be a clear liquid containing not more than 0.15 % insoluble matter, by 
weight.   
5.2 Sodium hypochlorite solution shall be miscible in water in all proportions.   
5.3 Sodium hypochlorite solution shall also, in addition to 5.1, conform to the requirements specified in Table 1, 
when tested in accordance with the tests specified therein.  
Table 1 — Requirements for sodium hypochlorite solutions   
S/N  Characteristic  Requirement  Method of test  
(i)  Insoluble matter, % by mass, max   0.15   Annex A    
(ii)  Available chlorine, % m/v, min.    10   Annex B    
(iii)  Total free alkali (as NaOH), % m/v, max.   1.5   Annex C    
(iv)  Iron (as Fe), ppm, max.   0.4   Annex D   
(v)  pH, min.    9   Annex E   DRS 353 -8: 2023  
3                ©RSB 2023  - All rights reserved  
  
6 Packaging and labelling  
6.1 Packaging  
Sodium hypochlorite solutions shall be packaged in suitable containers made of polyethylene or stainless steel 
which shall be properly sealed, appropriately vented and able to withstand normal usage and transportation.   
6.2 Labelling  
Containers shall be labelled legibly and indelibly with the following information:  
a) chemical name of the product indicating its intended use;   
b) name and address of manufacturer and/or trademark;   
c) instructions for use and safety precautions;   
d) batch or code number of the solution;   
e) net volume of the solution;   
f) per cent mass by volume of available chlorine;   
g) storage conditions;   
h) manufacture and expiry date and   
i) country of origin.   
 
 
 
 
 
.  
©RSB 2023  - All rights reserved                  4 
 Annex  A 
(normative)  
 
Testing for insoluble matter in sodium hypochlorite solution  
A.1 Procedure  
Pour approximately 100 ml of the sodium hypochlorite solution into a tared 400 ml beaker, place on a laboratory 
platform balance and weigh to the nearest 0.1 g. Add 100 ml of distilled water and mix thoroughly. Filter through 
a tared gooch crucible. Wash the beaker and the crucible with distilled water. Dry the crucible to the constant 
weight from 100°C to 105 °C  
A.2 Calculation  
Percent insoluble matter = mass of residue/mass of sample × 100  
 
 
 
 
 
 
 
 
 
 DRS 353 -8: 2023  
5                ©RSB 2023  - All rights reserved  
 Annex  B 
(normative)  
 
Determination of available chlorine  
B.1 Principle of test methods  
The sample is added to an acidified solution of potassium iodine and the released iodine titrated with standard 
sodium thiosulphate solution to the starch end point.   
B.2 Reagents   
B.2.1 Glacial acetic acid  
B.2.2 Standard potassium iodate solution — 0.1 N  
B.2.3 Starch indicator solution — 0.5. Mix 0.5 % of solution starch with 5 mL of cold water and add 95 mL of 
boiling water. Mix, cool and store in a glass bottle. Replace frequently or add 0.1 % m/v salicylic acid to the 
starch solution to minimize deterioration.   
B.2.4 Potassium iodine crystals — Iodate Free.   
B.2.5 Standard Sodium Thiosulphate Solution — 0.1 N.   
Dissolve 25 g of sodium thiosulphate (Na 2S2O3.5H 2O) crystals in freshly boiled and cooled water, and dilute to 
1 000 mL.   
NOTE The solution is more stable if the glassware is cleaned with sulphuric or chromic acids and thoroughly rinsed with water  
before use.   
B.3 Procedure   
B.3.1   Dissolve 2 g to 3 g of potassium iodide crystals in 50 mL of water in a 250 mL conical flask.   
B.3.2  Add 10 mL of glacial acetic acid, then pipette out a 3 mL aliquot of sample into the solution, keeping the 
tip of the pipette beneath the surface of the solution until drained.   
B.3.3  Titrate at once with 0.1 N standard sodium thiosulphate 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.  
  
©RSB 2023  - All rights reserved                  6 
 B.4 Calculation  
Available chlorine ( as Cl) percent mass by volume =  0.03546 × 100 × 𝐴𝑁
𝑉 
where,  
A = Volume in mL of standard sodium thiosulphate solution required for titration of the sample,   
N = Normality of the standard sodium thiosulphate solution, and  
 V = Volume in mL of original sample in aliquot used.  
  
  
  
  
  
  
  
  
  
 
 
 
 
 
 
 
 
 DRS 353 -8: 2023  
7                ©RSB 2023  - All rights reserved  
 Annex  C 
(normative)  
 
Determination of free alkali  
C.1 Principle of test method  
The sample solution is added to a neutralized, 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 phenol phthalein indicator.   
C.2 Reagents   
C.2.1 Barium chloride solution  — 100 g/L. Dissolve 100 g of barium chloride (BaCl2.2H2O) in water and dilute 
to one litre. Filter if turbid.   
C.2.2   Hydrochloric acid, standard  — 0.1 N.   
C.2.3   Hydrogen peroxide solution  — 3 %.   
C.2.4 Phenolphthalein indicator solution  — 0.5 %. Dissolve 0.5 g of phenolphthalein in 60 mL of 95 % ethyl 
alcohol and dilute to 100 mL with water.   
C.2.5   Sodium hydroxide solution  — 4 g/L.   
C.3 Procedure   
Place 50 mL of barium chloride solution and 30 mL of hydrogen peroxide solution in a 250 mL conical flask, add 
10 drops of phenolphthalein indicator solution, and neutralize with Na0H solution. Introduce into this neutral 
mixture 10 mL of the sample soluti on, shake or stir vigorously for one minute, and titrate the sodium hydroxide 
solution with 0.1 N HCl until the pink colour disappears.  
C.4 Calculation   
Free alkali as ( Na OH) g/L = 𝑉1× 𝑁× 40
𝑉 
where,  
V1= Volume, in mL of standard HCL required,   
N = Normality of the hydrochloric acid, and   
V = Volume, in mL of sample solution   
©RSB 2023  - All rights reserved                  8 
 Annex  D 
(normative)  
 
Determination of heavy metals (as Fe)  
D.1 Apparatus  
D.1.1  Nessler Cylinders — 50 mL capacity.   
D.2 Reagents   
D.2.1  Ammonium per Sulphate   
D.2.2 Butanoic potassium thiocyanate solution  — Dissolve 10 g of potassium thiocynate in 10 mL of water. 
Add suffiecient n -butonal to make up to 100 mL and shake vigorously till the solution is clear.   
D.2.3 Standard iron solution A — Dissolve 0.7202 g of ferrous ammonium sulphate in 100 mL of water, and 
5 mL of 1.5 (v/v) sulphuric acid and run in cautiously a dilute solution of potassium permangenate (0.2 % m/v) 
until a slight pink coloration remains after stirring well. Dilute with water to 1 000 mL and mix thoroughly. One 
millilitre of this solution contains 0.1 mg of iron as Fe.   
D.2.4 Standard iron solution B  — Taken 100 mL of standard iron solution A and dilute to 1 000 mL with water. 
One millilitre of this solution contains 0.01 mg of iron as Fe. This dilute solution shall be prepared fresh.   
D.3 Procedure   
D.3.1 Weigh 50.0 g of the sodium hypochlorite solution and evaporate it to dryness. Dilute it to 30 mL in a 
Nessler cylinder, add about 30 mg of ammonium persulphate and 15 mL of butanoic potassium thiocyanate 
solution. Make up to 50 mL, shake vigorously for abo ut 30 sec and allow the layers to separate. Carry out a 
control test in another Nessler cylinder using 2 mL of standard iron and solution B. Compare the intensity of the 
colour produced in the butanol layers in the two cylinders.   
D.3.2 The limit prescribed in Table 1 shall be taken as not having been exceeded if the intensity of colour 
produced with the sample is not greater than that produced in the control test.  
 
 
 
 
 DRS 353 -8: 2023  
9                ©RSB 2023  - All rights reserved  
 Annex  E 
(normative)  
 
Measurement of pH value  
E.1 Measure the pH,at room temperature, using a pH meter equipped with a glass electrode capable of 
measuring pH values  to an accuracy of 0.1 or better  
A= Reaction vessel  
B= 250 mL separating funnel  
C= Test tube  
D= Rubber tube  
E= Rubber stoppers  
 
Figure 1 — Apparatus for determination of sodium chlorate  
 
 
©RSB 2023  - All rights reserved                  10 
 Annex  F 
(normative)  
 
Determination of sodium chlorite  
F.1 Principle of method  
Sodium chlorate is reduced by sodium bromide in 8 N hydrochloric acid. After dilution and addition of potassium 
iodide, the released iodine (equivalent to hypochlorite plus chlorate) is titrated with standard sodium thiosulphate 
solution and starch indicat or.   
F.2 Apparatus   
The apparatus ( see Figure 1) consists of a 1 000 mL of wide mouth reaction bottle (A), fitted with a double hole 
rubber stopper carrying a separating funnel B, conveniently graduated or marked at 10,20 and 100 mL levels, 
and a delivery tube leading to a 50 mL test tube gas t rap C. The test tube trap is fitted with rubber tubing and a 
glass mouthpiece, D.   
F.3 Reagents   
F.3.1  Concentrated hydrochloric acid.   
F.3.2  Sodium bromide solution — 10 % w/v.   
F.3.3  Potassium iodine solution — 10 w/v.   
F.3.4  Standard sodium thiosulphate solution — 0.05 N.   
F.3.5  Starch  indicator solution — 0.5 % m/v.   
F.3.6  Sodium bicarbonate.   
F.3.7  Procedure   
F.3.7.1  Pipettee out a 3 mL aliquot of the sample into the reaction bottle (A), add one millilitre of concentrated 
hydrochloric acid and 0.3 g of pure sodium bicarbonate to expel all the air from the vessel through the long test 
tube C, containing a saturated sol ution of sodium bicarbonate. Then add 20 mL of sodium bromide solution 
followed by 80 mL of concentrated HCL.   
F.3.7.2 Stopper the bottle and shake well. Allow to stand for 10 minutes. Add 20 mL of 10 % m/v potassium 
iodide solution through the separating funnel carefully and titrate the liberated iodide against 0.05 N sodium 
thiosulphte solution using a few drops of a sta rch indictor solution. Turn a blank with all the reagents except the 
sample by proceeding in the same manner as that of the test.  DRS 353 -8: 2023  
11                ©RSB 2023  - All rights reserved  
 F.4 Calculate  
Sodium chlorate =(𝑎𝑠 𝑁𝑎𝐶𝑙𝑂 )𝑔
𝐿𝑥=(V2 – V1) × N × 17.75
V 
where,  
V2= Volume in mL of sodium thiosuSlphate used for the test;   
V1= Volume in mL of sodium thiosulphate used for the blank;   
N = Normality of sodium thiosulphate solution.  
V = Volume in mL of sample solution used  
F.5 Principle of method used  
Sodium chlorate is reduced by sodium bromide in 8 N hydrochloric acid. After dilution and addition of potassium 
iodide, the released iodine (equivalent to hypochlorite plus chlorate) is titrated with standard sodium thiosulphate 
solution and starch indicat or.  
  
 
 
 DRS 353 -8: 2023  
 
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