Reference number  
PDS 353-4: 2018  
© RSB 2018  
 
 
 RWANDA 
STANDARD  CD 
353-4 
 
First edition  
2018 -mm-dd 
Water quality  — Chemicals used for 
treatment of water intended for human 
consumption  — 
Part 4: 
Sodium Chloride  
  CD 353-4: 2018  
©RSB 2018 - 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 2018  
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 reprodu ce this document should be addressed to : 
Rwanda Standards  Board  
P.O Box 7099 Kigali -Rwanda  
KK 15 Rd, 49  
Tel. +250 788303492  
Toll Free: 3250  
E-mail: info@rsb.gov.rw  
Website: www.rs b.gov.rw   
ePortal: www.portal.rsb.gov.rw   CD 353-4: 2018  
iii                ©RSB 2018 - All rights reserved  
 Contents  Page 
1 Scope  ................................ ................................ ................................ ................................ .............  1 
2 Normative references  ................................ ................................ ................................ ...................  1 
3 Desc ription  ................................ ................................ ................................ ................................ .... 2 
3.1 Identification  ................................ ................................ ................................ ................................ . 2 
3.2 Commercial forms  ................................ ................................ ................................ ........................  2 
3.3 Physical properties  ................................ ................................ ................................ ......................  2 
3.4 Chemical properties  ................................ ................................ ................................ .....................  3 
4 Purity criteria  ................................ ................................ ................................ ................................  4 
4.1 General  ................................ ................................ ................................ ................................ ..........  4 
4.2 Composition of commercial product  ................................ ................................ ..........................  4 
4.3 Chemical parameters  ................................ ................................ ................................ ...................  5 
5 Test methods  ................................ ................................ ................................ ................................  5 
5.1 Sampling  ................................ ................................ ................................ ................................ ....... 5 
5.2 Analyses  ................................ ................................ ................................ ................................ ........  6 
6 Marking – Transportation – Storage  ................................ ................................ ...........................  9 
6.1 transportation  ................................ ................................ ................................ ...............................  9 
6.2 Markin g ................................ ................................ ................................ ................................ ..........  9 
6.3 Storage  ................................ ................................ ................................ ................................ ........  10 
Annex  A (informative)  General information on sodium chloride for electrochlorination by 
membrane cell  ................................ ................................ ................................ ............................  11 
A.1 Origin  ................................ ................................ ................................ ................................ ...........  11 
A.2 Chemical composition  ................................ ................................ ................................ ...............  11 
A.3 Use ................................ ................................ ................................ ................................ ...............  11 
 CD 353-4: 2018  
©RSB 2018 - All rights reserved                  iv 
 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.  
PDS 353-4 was prepared by Technical Committee RSB/TC 013, Water and Sanitation ,  
In the preparation of this standard, reference was made to the following standard  (s): 
BS EN 16370:2013:  Chemicals used for treatment of water intended for human consumption —Sodium chloride 
for onsite electrochlorination using membrane cells  
The assistance de rived from the above source is hereby acknowledged with thanks.  
PDS 353 consists of the following parts, under the general title Water quality  — Chemicals used for treatment 
of water intended for human consumption : 
 Part 1: Aluminium sulfate  
 Part 2: Calcium hypochlorite  
 Part 3: Sodium chlorate  
Part 4: Sodium chloride  
  CD 353-4: 2018  
v                ©RSB 2018 - All rights reserved  
 Committee membership  
The following organizations were represented on the Technical Committee on Water and Sanitation  (RSB/TC 
013) in the preparation of this standard.  
Integrated Polytechnic Regional Centre/Kigali ( IPRC -Kigali ) 
Rwanda Utility Regulatory Authority (RURA)  
SULFO Rwanda  Ltd 
Rwanda Association of Professional Environmentalist Practitioners (RAPEP)  
Shine Engineers Multisectorial Company Ltd (SEMC  
Rwanda Fisheries Sector ( RSF) 
Water and Sanitation Corporation Ltd (WASAC)  
Rwanda  Standards Board  (RSB) – Secretariat  CD 353-4: 2018  
©RSB 2018 - All rights reserved                  vi 
 Introduction  
Treatment of water intended for human consumption can be achieved by using various chemicals which might 
raise the risk of cancer or cause other health hazards by creating toxic by -products that need tighter control in 
order to avoid those risks and meets requirements of drinking water as stated in RS EAS 153  
Chemicals used during treatment of water have to be of good quality and meet standards requirement, in or der 
to avoid any contamination of water by impurities of these chemicals and therefore ensure a successful water 
treatment  
 CD 353-4: 2018  
1                ©RSB 2018 - All rights reserved  
 Water quality  — Chemicals used for treatment of water intended 
for human consumption  — Part 4: Sodium chloride  
1 Scope  
This Committee Draft  Rwanda Standard is applicable to sodium chloride intended for onsite electrochlori nation 
of water intended for human consumption It describes the characteristics and specifies the requirements and 
the corresponding test methods for sodium chloride . It also gives information on its use in water treatment . 
2 Normative references   
The following documents are referred to in the text in such a way that some or all of  their content constitutes 
requirements of this document.  For dated references, only the edition  cited applies. For undated references, the 
latest edition of the reference d document (including any amendments) applies.  
ISO 3696 , Water for analytical laboratory use — Specification and test methods (ISO 3696)  
ISO 2479 , Sodium chloride for industrial use — Determination of matter insoluble in water or in acid and 
preparation o f principal solutions for other determinations  
ISO 2480 , Sodium chloride for industrial use — Determination of sulphate content — Barium sulphate 
gravimetric method  
ISO 2482 , Sodium chloride for industrial use — Determination of calcium and magnesium con tents — EDTA 
complexometric methods  
ISO 2483 , Sodium chloride for industrial use — Determination of the loss of mass at 110 °C  
ISO 316 5, Sampling of chemical products for industrial use — Safety in sampling  
ISO 6206 , Chemical products for industrial use  — Sampling — Vocabulary  
ISO 6227 , Chemical products for industrial use — General method for determination of chloride ions — 
Potentiometric method  
ISO 8213,  Chemical products for industrial use — Sampling techniques — Solid chemical products in the form  
of particles varying from powders to coarse lumps . 
ISO 11885 , Water quality -- Determination of selected elements by inductively coupled plasma optical emission 
spectrometry (ICP -OES)  
ISO 17378 -2, Water quality -- Determination of arsenic and antimony -- Part 2: Method using hydride generation 
atomic absorption spectrometry (HG -AAS)   
©RSB 2018 - All rights reserved                  2 
 3 Description  
3.1 Identification  
3.1.1  Chemical name  
Sodium chloride.  
3.1.2  Synonym or common name  
Salt. 
3.1.3  Relative molecular mass  
58.45 for sodium chloride.  
3.1.4  Empirical formula  
NaCl.  
3.1.5  Chemical formula  
NaCl.  
3.2 Commercial forms  
These products are available as rock salt, sea salt or evaporated salt, and it is supplied as free -flowing crystals 
or their compacted forms.  
3.3 Physical properties  
3.3.1  Appearance  
The product is white and crystalline.  
3.3.2  Density  
The density of the solid crystal is 2 .16 g/cm3 at 20 °C.  
The bulk density depends on the particle size distribution.  
3.3.3  Solubility (in water)  
The solubility of the product depends on the temperature as given in Figure 1.  CD 353-4: 2018  
3                ©RSB 2018 - All rights reserved  
  
Key 
1 Transition point  
NaCl → NaCl.2H 2O Temperature  °C NaCl solution  Mass 
fraction in g/100g  
- 10 25.0 
0 26.34 
10 26.35 
20 26.43 
30 26.56 
40 26.71 
50 26.89 
60 27.09 
70 27.30 
80 27.53 
90 27.80 
100 28.12 
Figure 1 - Solubility curve for sodium chloride in water  
3.3.4  Melting point at 100kPa  
801 °C for sodium chloride.   
3.3.5  Specific heat  
Approximately 850 J/(kg K) at 25 °C for the solid.   
3.3.6  Viscosity (dynamic)  
The viscosity of the saturated solution at 20 °C is approximately 1 .9 mPa .s.1  
3.3.7  Physical hardness  
The hardness of solid salt is given as 2 to 2 .5 on the Mohs' scale of hardness.  
3.4 Chemical properties  
Sodium chloride is stable, non -volatile and aqueous solutions have good electrical conductivity.  
                                                   
1 1 Centipoise = 1 mPa.s (Millipascal  Second)  
 
©RSB 2018 - All rights reserved                  4 
 Sodium chloride reacts with a number of acids (e.g. sulfuric acid, ph osphoric acid) and strong oxidising agents. 
The reactions are often complex and require heat for completion.  
NOTE  Under certain conditions, a sodium chloride solution can cause corrosion of metallic surfaces  
4 Purity criteria  
4.1 General   
4.1.1 This Standard specifies the minimum purity requirements for sodium chloride for onsite 
electrochlorination of water intended for human consumption. The basic quality of the applied salt shall meet 
the requirements of Codex Alimentarius for Food Grade Salt . 
4.1.2  chemica ls produced by this process is chlorine or sodium hypochlorite,  attention shall be paid to the 
minimization of likely impurity commonly present in the product.  
4.1.3  Users of the product sh all check the national regulations in order to clarify whether it is allowed/not 
banned and is of appropriate purity for treatment of water intended for human consumption, taking into account 
raw water quality, required dosage, contents of other impurities an d additives used in the product not stated in 
the product standa rd, and other relevant factors.  
4.2 Composition of commercial product  
The content of sodium chloride in the dry product shall not be less than:  
 grade 1: mass fraction 99,4 % of dry NaCl;  
 grade 2: mass fraction 98,5 % of dry NaCl.  
NOTE An anticaking agent, sodium or potassium hexacyanoferrate  [Fe(CN) 6]−4, is not allowed.  Impurities and by -
products  
The product shall conform to the requirements specified in Table 1.  
Table 1 — Impurities and by -products  
Impurity/by -product  
 Limit in mass fraction of NaCl content (mg/kg)  
Test methods  
Grade 1  Grade 2  
Moisture, dry product  ≤ 1 000  ≤ 1 000  
See 5.2.2.2  
Moisture, wet product  ≤ 50 000 (a)  ≤ 50 000  
Water -insoluble matter  ≤ 500  ≤ 1000  See 5.2.2.1  
Bromide  ≤ 50 ≤ 250  See 5.2.2.3  
Iron  ≤ 2 ≤ 2 ISO 11885  CD 353-4: 2018  
5                ©RSB 2018 - All rights reserved  
 Manganese  ≤ 0,5  ≤ 1 
Calcium + magnesium  ≤ 25 ≤ 300  ISO 2482  
Sulfate  ≤ 400  ≤ 600  ISO 2480  
NOTE The flowability  of the products is reduced by a high moisture content; further information should be  availed by  the 
supplier of the product.  
NOTE  The grade should be selected based on the requirements of the electrochlorination equipment depending on 
the susceptibility  of the membrane to fouling. The electrochlorination equipment manufacturers will specify which grade can 
be used to meet the requirements of the Drinking Water standards.  
4.3 Chemical parameters  
The products shall conform to the requirements specified in Table 3.  
  
Table 3 — Chemical parameters  
Parameter  Limits in mg/kg of 
commercial product  Test method  
Arsenic (As)  ≤ 0,3  ISO 17378 -2 
Cadmium (Cd)  ≤ 0,5  
ISO 11885  Chromium (Cr)  ≤ 0,5  
Nickel (Ni)  ≤ 0,5  
Lead (Pb)  ≤ 2  
Antimony (Sb)  ≤ 2  
Selenium (Se)       ≤ 2  
Mercury (Hg)  ≤ 0,1  
 ISO 12846  
5 Test methods  
5.1 Sampling  
A test sample of about 500 g shall be taken for analysis, ensuring that it is representative of the whole batch, 
and taking account of ISO 3165 and ISO 6206. Prepare the laboratory sample(s) required in accordance with 
ISO 8213.   
©RSB 2018 - All rights reserved                  6 
 5.2 Analyses  
5.2.1  Main product  
The mass fraction in % of sodium chloride (NaCI) shall be determined by calculation, on the basis of the resu lts 
of the determinations of sulfate (according to ISO 2480), halogens (according to ISO 6227), calcium and 
magnesium (according to ISO 2482), and loss of mass on drying (according to ISO 2483). Convert sulfate to 
calcium sulfate and unused calcium to calc ium chloride, unless sulfate in sample exceeds the amount necessary 
to combine with calcium, in which case convert calcium to calcium sulfate and unused sulfate to first to 
magnesium sulfate and the remaining sulfate to sodium sulfate. Convert unused magne sium to magnesium 
chloride. Convert unused halogens to sodium chloride. Report the sodium chloride contents on a dry matter 
basis, multiplying the mass fraction in % of sodium chloride by 100 / (100 - P), where P in the percentage of the 
loss of mass on dry ing (see 5.2.2.2).  
5.2.2  Impurities  
5.2.2.1  Water -insoluble matter  
The content of water -insoluble matter shall be determined in accordance with ISO 2479.   
5.2.2.2  Moisture content  
The loss of mass at 110 °C shall be determined in accordance with ISO 2483.  
5.2.2.3  Bromide  
5.2.2.3.1  General  
The present method describes a titrimetric method with sodium thiosulfate for the determination of total bromine 
and iodine in sodium chloride. The method is applicable to products of bromine and iodine content (expressed 
conventionally as bromide, Br-) equal to or greater than 3 mg bromine per kilogram of salt. Bromine or bromide 
are equivalent for the expression of the results.   
5.2.2.3.2  Principle  
The sample is dissolved in water. Oxidation of iodide to iodate and bromide to bromate is achieved with 
hypochlorite in a buffered medium and the excess of oxidant is eliminated with formic acid. Free iodine, 
equivalent to the amount of the present iodate and bromate, is formed by addition of hydrochloric acid and 
potassium iodide. The free iodine is titrated with sodium  thiosulfate using starch as indicator.  
5.2.2.3.3  Reactions  
I- + 3 ClO- → IO 3− + 3 Cl-                 (1)  
Br- + 3 ClO - → BrO 3− + 3 Cl-               (2) 
Titration of the iodate and bromate follows the reactions:  CD 353-4: 2018  
7                ©RSB 2018 - All rights reserved  
 IO3− + 6 I- + 6 H+ → 3 I 2 + I- + 3 H 2O              (3) 
BrO 3− + 6 I- + 6 H+ → 3 I 2 + Br- + 3 H 2O              (4) 
NOTE  Reactions (1) and (2) require for completion the presence of chloride ions that are added into the buffer solution.   
5.2.2.3.4  Reagents  
Unless otherwise stated, use only reagents of recognised ana lytical grade and only water conforming to grade 
3 in accordance with ISO 3696.  
5.2.2.3.4.1  Calcium carbonate , precipitated.  
5.2.2.3.4.2  Hydrochloric acid , c(HCl) ≈ 4 mol/l.  
5.2.2.3.4.3  Formic acid , c(HCOOH) ≈ 3 mol/l.  
5.2.2.3.4.4  Potassium iodide , β(KI) ≈ 100 g/l.  
Prepare this solution on the day of use and store it in a dark bottle.  
5.2.2.3.4.5  Sodium hypochlorite , β(NaClO) ≈ 19 g/l.  
Prepare this solution by dilution of a concentrated technical sodium hypochlorite solution. Renew the solution 
each week.  
Commercial household solutions which can contain interfering additives should not be used.  
5.2.2.3.4.6  Buffer solution  
Dissolve 50  g of sodium dihydrogen orthophosphate dihydrate, (NaH 2PO 4·2 H 2O), 50 g of disodium hydrogen 
orthophosphate dodecahydrate (Na 2HPO 4·12 H 2O), 50 g of tetrasodium pyrophosphate decahydrate 
(Na 4P2O7·10 H 2O) and 150 g of sodium chloride (see note) in 650 ml of water .  
NOTE  As the same quantity of buffer solution is used for the sample and for the blank test solution, it is not necessary 
to use products completely free of iodine and bromine.  
5.2.2.3.4.7  Sodium thiosulfate, standard volumetric solution , c(Na 2S2O3) = 0,01 mol/l.  
Prepare this solution by dilution of a standard volumetric solution c(Na 2S2O3) = 0,1 mol/l and standardise with a 
potassium iodate solution [c(1/6 KIO 3) = 0,01 mol/l].  
5.2.2.3.4.8  Methyl red , 0,5 g/l solution in volume fraction 95 % eth anol.  
5.2.2.3.4.9  Starch solution , 2 g/l solution.   
©RSB 2018 - All rights reserved                  8 
 Prepare this solution at the time of use from soluble starch.  
5.2.2.3.5  Apparatus  
Ordinary laboratory apparatus and:  
5.2.2.3.5.1  Burette  allowing the distribution and measurement of 0,01 ml.  
5.2.2.3.6  Procedure  
5.2.2.3.6.1  Test portion  
Weigh, to the nearest 0,1 g, about 40 g of the test sample.  
For bromine plus iodine content greater than 200 mg per kilogram of salt, the test portion should be reduced 
accordingly.  
5.2.2.3.6.2  Test solution  
Transfer the test portion (5.2.2.3.6.1) and 150 ml of water into a 500 ml conical flask, stir to dissolve.  
5.2.2.3.6.3  Blank test solution  
Transfer 150 ml of water into a 500 ml conical flask.  
5.2.2.3.6.4  Determination  
Proceed with the conical flasks prepared in (5.2.2.3.6.2) and (5.2.2.3.6.3) in the following way.  
Add 4 drops of methyl red (5.2.2.3.4.8) and hydrochloric acid (5.2.2.3.4.2) until the solution turns red. Neutralise 
by addition of calcium carbonate (5.2.2.3.4.1) to a permanent slight cloudiness.  
Add 6,0 ml of buffer solution (5.2.2.3.4.6) and 5,0 ml of  sodium hypochlorite solution (5.2.2.3.4.5). Heat to (90 
± 2) °C with agitation to avoid local overheating and keep at this temperature for 20 min.  
Add 10 ml of formic acid (5.2.2.3.4.3) and swirl. When CO 2 ceases to evolve, cool to about 20 °C, add 2,0 m l of 
potassium iodide solution (5.2.2.3.4.4) and 25 ml of hydrochloric acid (5.2.2.3.4.2). Swirl and allow to stand for 
1 min.  
Titrate with the sodium thiosulfate standard volumetric solution 0,01 mol/l (5.2.2.3.4.7) using a burette 
(5.2.2.3.5.1). When th e solution is nearly discoloured, add 1 ml of starch solution (5.2.2.3.4.9) and continue the 
titration until the blue colour disappears during at least 30 s.  
The presence of oxidising agents can lead to inaccurate results. The Fe3+ interference can be avo ided by 
complexation with EDTA. An automatic titrator provided with a platinum electrode and an Ag/AgCl reference CD 353-4: 2018  
9                ©RSB 2018 - All rights reserved  
 electrode can be used. In this case, the addition of starch solution (5.2.2.3.4.9) during the determination should 
be avoided.  
5.2.2.3.7  Expression of results  
5.2.2.3.7.1  Method of calculation  
The bromine plus iodine content of the sample, w(Br), expressed as milligrams of bromine per kilogram of salt, 
is given by the following formula:  
𝑤𝐵𝑟 =13,318  ×𝑐(𝑁𝑎 2𝑆2𝑂3)×+1000
𝑚×(𝑉1−𝑉0) 
where  
m  is the mass, in grams, of the test portion (5.2.2.3.6.1);  
V1  is the volume, in millilitres, of sodium thiosulfate (5.2.2.3.4.7) used for the titration of the test  solution 
(5.2.2.3.6.2);  
V0  is the volume, in millilitres, of sodium thiosulfate (5.2.2.3.4.7) used for the titration of the  blank test 
solution (5.2.2.3.6.3);  
c(Na 2S2O3) is the concentration in moles per litre of the sodium thiosulfate standard volumetric solution  
(5.2.2.3.4.7). c(Na2S2O3) 
6 Marking  – Transportation – Storage  
6.1 transportation   
Sodium chloride is not classified as a dangerous product for road, rail, sea and air transportation.  
Sodium chloride shall be delivered in bulk or in bags.  
In order that the purity of the product is not affected, the means of delivery shall not have been used previously 
for any different product or it shall have been specially cleaned and prepared before use.  
6.2   Marking  
The marking shall include the following information:  
a) the name "Sodium chloride, salt for electrochlorination , "dry salt" or "undried salt" and trade name;  
b) net mass;  
c) density/concentration ;   
©RSB 2018 - All rights reserved                  10 
 d) name and the address of the supplier and/or manufacturer ;  
e) statement of conformity to the standard ; 
f) Shelf life ; 
g) Storage conditions ; and  
h) Batch number  
The supplier shall provide a certificate of analysis against the standards  and the material Safety Data sheet  
Note  the user should verify the relevance of that certificate  
6.3 Storage  
6.3.1  Long term stability  
Sodium chloride is stable during long -term storage, providing it is kept in a dry place.  
6.3.2  Storage incompatibilities  
Sodium chloride shall be stored in covered and dry conditions to avoid any risk of contamination.  
The product shall not be allowed to come into contact with strong acids, e.g. sulfuric acid or phosphoric acid.  
 CD 353-4: 2018  
11                ©RSB 2018 - All rights reserved  
 Annex  A 
(informative)  
 
General information on sodium chloride for electrochlorination by 
membrane cell  
A.1 Origin  
a) Rock salt: Salt produced by mining salt deposits of different geological formations derived from ancient 
seas.  
b) Sea salt: Salt produced by sea water eva poration via the action of sun and wind.  
c) Evaporated salt: Salt produced by evaporating water from a salt solution in a sp ecial evaporator leading to 
the recrystallisation of the salt.  
A.2 Chemical composition  
A.2.1  Organic components of sodium chloride can also affect equipment efficiency. As these requirements 
can vary considerably, both equipment and salt suppliers should be consulted when selecting salt for this 
application.  
The organic content should be limited, as it can form halogen -organic compounds.  If necessary, it should be 
explained which type of salt is concerned, especially rock salt and sea salt.  
A.2.2  It should also be noted that the quality of water used in preparing salt solutions for this application might 
also need to be taken into accoun t when selecting the salt to be used.  
A.2.3  The sodium chlorate (NaClO 3) content of the sodium hypochlorite produced should not exceed a mass 
fraction  of 5,4 % of available chlorine.  
NOTE  Sodium chlorate is a by -product of the manufacturing process and ca n be formed during storage.  
The treated water should not contain more than 700 μg/l chlorate.  
A.3 Use   
A.3.1  Function  
Salt to be used to produce active chlorine (Cl 2 or NaClO) by electrolysis of the brine for disinfection of the water.  
A.3.2  Form in which the product  is used  
It is used in the form of a saturated solution.   
©RSB 2018 - All rights reserved                  12 
 A.3.3  Consumption of salt for electrochlorination  
The consumption is variable and depends on the applied technique, and is typically in the range of 1,7 kg to 3 
kg of NaCl per kilogram of chlorine.  
A.3.4  Means of application  
To be documented by the equipment supplier.  
A.3.5  Secondary effects  
 Increase of the chloride content;  
 in some cases,  formation of halomethanes.  
A.3.6  Spillage  
The product should be collected, then the area should be rinsed with plenty of water.  
A.3.7  Fire  
Sodium chloride is not combustible .  CD 353-4: 2018  
13                ©RSB 2018 - All rights reserved  
 Bibliography  
[1] RS 127 -1, Bleaching agents — Specification — Part 1: Sodium hypochlorite solutions for water treatment  
 
[2]  
. 
 CD 353-4: 2018  
ICS 71.100.80  
 
 
©RSB 2018 - All right s reserved