Quality of Domestic Water Supplies Assessment Guide PDF

Quality of Domestic Water Supplies: Assessment Guide Dr PP Mpungose Office: 2.20B, D6 Campus E-mail: [email protected] 1 2  SECTION 1: GENERAL INFORMATION ON THE CONCEPTS OF WATER QUALITY Familiarise yourself with the Wh...

Quality of Domestic Water Supplies: Assessment Guide Dr PP Mpungose Office: 2.20B, D6 Campus E-mail: [email protected] 1 2  SECTION 1: GENERAL INFORMATION ON THE CONCEPTS OF WATER QUALITY Familiarise yourself with the Where does the What is water What is water concept of water water come from? quality? pollution? quality How does water What is domestic Who uses water? quality affect the use of water? domestic user? 3 WHERE DOES WATER COME FROM ? The fresh water we use for drinking, washing, and for preparing food comes from: rainwater, surface water sources (such as rivers or dams), or groundwater sources (such as boreholes and springs). The amount of fresh water is limited and it continuously repeats its journey through the water cycle. 4  WHAT IS WATER QUALITY ? The term "water quality" is used to describe the microbiological, physical and chemical properties of water that determine its fitness for use. Microbiological quality Physical quality Chemical quality Many of these properties are controlled or influenced by substances which are either dissolved or suspended in the water. 5  WHAT IS WATER QUALITY ? 1. MICROBIOLOGICAL QUALITY: Refers to the presence of organisms that cannot be seen by the naked eye, such as protozoa, bacteria and viruses. Many of these microbes are associated with the transmission of infectious waterborne diseases such as gastro-enteritis and cholera. Since it is difficult and costly to detect these microbes (pathogens), it is common practice to use microbiological indicators as an indication of recent faecal pollution and the potential risk of infectious diseases from the water. Faecal and total coliforms are commonly used as indicators to determine the microbiological quality of domestic water supplies. 6  WHAT IS WATER QUALITY ? 2. PHYSICAL QUALITY: Refers to water quality properties that may be determined by physical methods such as conductivity, pH and turbidity measurement. The physical quality mainly affects the aesthetic quality (taste, odour and appearance) of water. 3. CHEMICAL QUALITY: Refers to the nature and concentration of dissolved substances such as salts, metals and organic chemicals. Many chemical substances in water are essential as part of the daily intake required, but at high concentrations they make water unpalatable and cause illnesses. 7  WHAT IS WATER POLLUTION? WHAT IS WATER POLLUTION? Water pollution occurs when water is rendered less fit for use as a result of human activities. Where human activity occurs, wastes may get into the water source. These wastes can pose serious risks for domestic water users. Human activities that typically cause problems for domestic water quality are: intensive irrigation, mining activities, industries, and dense human settlements (particularly if these settlements have poor sanitation facilities). Domestic water quality is affected by nearby human activities which may pollute the water, as well as by natural geological conditions in the area. 8  WHO USES WATER ? Water users can he divided into four main categories: domestic users (e.g., drinking, food preparation washing clothes, bathing and gardening), recreational users (e.g., swimming, fishing), industrial users (e.g., power generation, process water), and agricultural users (e.g., watering of crops, water for animals ). The environment also requires water if it is to survive. This includes water for animals and fish living in the water, as well as for plants growing in rivers or streams, or next to them. The aquatic environment is part of the resource. 9  WHAT IS DOMESTIC USE OF WATER ? Domestic water is used for a number of purposes in and around the home. These are: for survival - drinking and food preparation, for personal hygiene - washing clothes, bathing and sewage removal, and for gardening - watering a vegetable patch or beautifying the surroundings. 10  HOW DOES WATER QUALITY AFFECT THE DOMESTIC USER? Water quality affects the domestic user in terms of: health, aesthetics (the appearance of the water or the effects it has on clothes and household fixtures such as baths), and economics (replacement of pipes, hot water geysers, etc.). The health effects of water quality on the user can be divided into two types: 1. ACUTE EFFECTS: Effects that can be seen after a very short time. 2. CHRONIC EFFECTS: Effects that show only after the water has been used for a long time. 11 SECTION 2: COLLECT AND PROCESS THE DATA Where should the What substances Determine the quality of domestic are important for minimum data water supply be domestic water needs assessed? users? How frequently Which substances should the must be included substances be in the assessment? measured? 12  COLLECTING AND PROCESSING THE DATA 1. DETERMINE THE MINIMUM DATA NEEDS a) Identify sampling point. b) Determine which substances are important. c) Determine which substances must be included. d) Determine minimum data required. 2. COLLECT DATA Collect samples and analyse, or consult existing databases. 3. PROCESS THE DATA Process the data for each substance: (a) Identify the maximum value. (b) Calculate the average value. 13  COLLECTING AND PROCESSING THE DATA: DETERMINE THE MINIMUM DATA NEEDS 1. Determine the minimum data needs (a) Where should the quality of domestic water supply be assessed? It is important to assess the quality of the water supplied at all points in the water supply system. The water supply system consists of the: water source, the water treatment works and the distribution system up to the point of use. At the minimum, samples should be taken from: the source of the water, the outflow from the treatment works (if the water is treated), and at the point of use. 14 THE WATER SUPPLY SYSTEM SHOWING THE POINTS THAT SHOULD BE SAMPLED TO ASSESS DOMESTIC WATER QUALITY. (a) Identify sampling point. 15  COLLECTIMG AND PROCESSING THE DATA: DETERMINE THE MINIMUM DATA NEEDS (b) What substances are important for domestic water users ? A great many substances can be found in water. However, only a few of these commonly occur in concentrations high enough to be of concern to domestic water users. The most important substances to measure are those that often occur in concentrations high enough to cause health, aesthetic or other problems. 16  COLLECTING AND PROCESSING THE DATA: DETERMINE THE MINIMUM DATA NEEDS (b) What substances are important for domestic water users? Table 1A: Substances which are general indicators of water quality GROUP A Electrical conductivity (total dissolved salts) Conductivity is an indicator of total dissolved salts (TDS), and also establishes if the water is drinkable and capable of quenching thirst. Faecal coliforms This is an indicator of the possible presence of disease-causing organisms. It establishes if water is polluted with faecal matter. pH value This has a marked effect on the taste of the water and also indicates possible corrosion problems and potential copper, zinc and cadmium problems. Turbidity This affects the appearance, and thus the aesthetic acceptability, of the water. Turbidity is commonly high in surface waters. Free available chlorine (Residual chlorine) This is a measure of the effectiveness of the disinfection of the water. Residual chlorine is the chlorine concentration remaining at least 30 minutes after disinfection. There should be residual chlorine in the water, but if concentrations are too high it may impart an unpleasant taste and smell to the water. Group A substances are indicators of potential problems and should be frequently tested at all points in the water supply system, irrespective of the source of the water. (Free available (or residual) chlorine has to be measured only if the water has been treated with chlorine-based disinfectants.) 17  COLLECTING AND PROCESSING THE DATA: DETERMINE THE MINIMUM DATA NEEDS (b) What substances are important for domestic water users? Table 1B: Substances which are commonly present at concentrations which may lead to health problems GROUP B Nitrate & nitrite These are common in groundwater (borehole) samples, particularly in areas of intensive agricultural activity, or where pit toilets are used. Severe toxic effects are possible in infants. Fluoride This is often elevated in groundwater in hot, arid areas. Can cause damage to the skeleton and the marking of teeth. Sulphate This is particularly common in mining areas. Causes diarrhoea, particularly in users not accustomed to drinking water with high sulphate concentrations. Chloride This is often elevated in hot, arid areas, and on the western and southern Cape coasts (particularly in groundwater). May cause nausea and vomiting at very high concentrations. Arsenic This may be present in groundwater, particularly in mining areas. Can lead to arsenic poisoning. Total coliforms This provides an additional indicator of disease-causing organisms, and the effectiveness of disinfection. The presence/concentration of Group B substances should be determined before the water is supplied. The frequency of testing depends on the source and the treatment applied. Note that substances of concern due to pollution sources in the 18 area, may have to be added to Group B.  COLLECTING AND PROCESSING THE DATA: DETERMINE THE MINIMUM DATA NEEDS (b) What substances are important for domestic water users? Table 1C: Substances which occur less frequently at concentrations of real concern to health GROUP C Cadmium This usually occurs along with zinc in acidic waters where it may have been dissolved from appliances. Copper This affects the colour of the water and can cause upset stomachs. Normally occurs only when copper piping is used to carry water with a low pH value. Group C substances should be tested for at point of use only in areas of the country where soft water of a low pH value is used. 19  COLLECTING AND PROCESSING THE DATA: DETERMINE THE MINIMUM DATA NEEDS (b) What substances are important for domestic water users? Table 1D: Substances which may commonly be present at concentrations of aesthetic or economic concern in domestic water sources GROUP D Manganese This is common reason for brown or black discolouration of fixtures and for stains in laundry. Can be common in bottom waters of dams, or in mining areas. Zinc This affects the taste of water. Usual cause is acidic water dissolving zinc from galvanised pipes or from appliances. Iron This affects the taste of the water and may also cause a reddish brown discolouration. Can be common in bottom waters of dams, or in mining areas. Can cause growth of slimes of iron reducing bacteria that ultimately appear as black flecks in the water. Potassium This affects the taste of the water and is bitter at elevated concentrations. Sodium This affects the taste of the water. Often elevated in hot, arid areas and on the western and southern Cape coasts (particularly in groundwater). Calcium This can cause scaling and can reduce the lathering of soap. Magnesium This affects the taste of the water. It is bitter at high concentrations. Common in some areas it adds to the effect of calcium. Hardness, Total This is a combination of calcium and magnesium. It is associated with scaling and inhibition of soap lathering. The presence of Group D substances should be determined at least when assessing the water for the first time. 20 Thereafter they can be included when there is reason to believe that their concentrations may have changed.  COLLECTING AND PROCESSING THE DATA: DETERMINE THE MINIMUM DATA NEEDS (c) Which substances must be included in the assessment? A number of factors influence the choice of substances (also called variables or constituents) which should be included in the assessment. These are: where are you assessing the water? (i.e., at the source, the treatment works, or at the point of use), what is the source of the water? (i.e., river, stream, well, borehole, dam or rainwater tank), what pollution problems may occur in the area?, and what problems have been experienced with similar sources in the vicinity? 21 TABLE 2: THE SUBSTANCES WHICH MUST BE INCLUDED WHEN ASSESSING DOMESTIC WATER QUALITY AT DIFFERENT POINTS IN THE SUPPLY SYSTEM, AND FROM DIFFERENT SOURCES 22  HOW FREQUENTLY SHOULD THE SUBSTANCES BE MEASURED? (d) Determine minimum data required. The concentrations of the substances in water are never constant. In general, the more often a substance is measured, the more reliable the assessment of the water quality will be. Table 2: The minimum and recommended numbers of samples and sampling frequencies for different points in the water supply system MINIMUM RECOMMENDED SAMPLING POINT Number of Sampling Number of samples Sampling frequency Samples / year frequency / year S River/stream/spring/well 4 3 - monthly 26 2 - weekly O U Dam 2 6 - monthly 12 1 - monthly R C Borehole 1 - 2 6 - monthly E Treatment works 4 3 - monthly 12/52/365' monthly/weekly/daily1 Point of use 4 3 - monthly 12/52/365' monthly/weekly/daily1 23 1 Depends on size of treatment works, the variability in the water quality and the number of people supplied with water.  COLLECTING AND PROCESSING THE DATA: COLLECT THE DATA COLLECT THE DATA How is data obtained? The collection and analysis of samples is possibly one of the most important steps in the process of assessing the quality of domestic water supplies. This should be done in the correct way to ensure reliable water quality data. (a) Collection of samples It is important to collect samples in both the wet and dry seasons to ensure that the full range of possible conditions is assessed. (b) Analysis of samples It is important to use a reliable laboratory to analyse the samples. 24  COLLECTING AND PROCESSING THE DATA: PROCESS THE DATA PROCESS THE DATA How must water qualify data be processed? The water quality data is processed by: taking the maximum (highest) concentration to determine acute effects, and calculating the average concentration to determine chronic effects. 25  THE PROCESSING OF THE WATER QUALITY DATA FOR THE ASSESSMENT. Collect all the available water quality data for the last year Check to see if you have the minimum number of samples and the correct substances Take the highest value of Maximum value each substance Repeat for each substance Calculate the average value Average value for each substance 26  A STEP-BY-STEP PROCEDURE FOR CLASSIFYING WATER 1. COMPARE RESULTS TO GUIDELINES (a) Select first substance. (b) Compare maximum value to guideline for each use. (c) Note class, e.g., blue, green, yellow, red or purple. (d) Compare average value (if available and applicable) to guideline for each use. (e) Note class, e.g., blue, green, yellow, red or purple. 2. CLASSIFY WATER PER SUBSTANCE (a) Identify the worst class for each substance for both the maximum and the average values (b) Classify the water per substance according to Table 5, p 25. 3. DETERMINE THE OVERALL CLASS OF WATER SOURCE The worst class determines the overall class. (See case study, p 26) 27  CLASSIFY THE WATER (A) WHY CLASSIFY WATER? Water is classified to: establish how suitable it is to the various domestic uses, namely drinking, food preparation, bathing and for washing clothes, make it easy to communicate water quality information to the public and other role players, and to aid in decision-making regarding the management of the quality of domestic water supplies. 28  CLASSIFY THE WATER (b) HOW DOES THE CLASSIFICATION SYSTEM WORK? The classification system describes the effects of increasing concentrations of each of the substances considered important for domestic use. The system uses a simple colour and number code ranging from ideal to totally unacceptable water quality. The guidelines are presented in terms of a simple colour-coded classification system for the substances outlined in the previous section as important for domestic users. The classification is based on increasing concentrations of these substances, and allows for classifying the: health effects of water used for drinking, as well as aesthetic effects of water used for drinking, health and aesthetic effects of water used for food preparation, health and aesthetic effects of water used for bathing, and the health and aesthetic effects of water used for washing clothes. 29  CLASS/COLOUR DESCRIPTION EFFECTS Table 3: Structure of the classification system describing the effects of the different classes of water on the various domestic uses of water Class 0 / blue Ideal water quality Drinking Health: No effects, suitable for many generations. Drinking Aesthetic: Water is pleasing. Food preparation: No effects. Bathing: No effects. Laundry: No effects. Class 1 / Green Good water quality Drinking Health: Suitable for lifetime use. Rare instances of sub-clinical effects. Drinking Aesthetic: Some aesthetic effects may be apparent. Food preparation: Suitable for lifetime use. Bathing: Minor effects on bathing or on bath fixtures. Laundry: Minor effects on laundry or on fixtures. Class 2 / Yellow Marginal water quality Drinking Health: May be used without health effects by the majority of individuals of all ages, but may cause effects in some individuals in sensitive groups. Some effects possible after lifetime use. Drinking Aesthetic: Poor taste and appearance are noticeable. Food preparation: May be used without health or aesthetic effects by the majority of individuals. Bathing: Slight effects on bathing or on bath fixtures. Laundry: Slight effects on laundry or on fixtures. Class 3 / red Poor water quality Drinking Health: Poses a risk of chronic health effects, especially in babies, children and the elderly. Drinking Aesthetic: Bad taste and appearance may lead to rejection of the water. Food preparation: Poses a risk of chronic health effects, especially in children and the elderly. Bathing: Significant effects on bathing or on bath fixtures. Laundry: Significant effects on laundry or on fixtures. Class 4 / Purple Unacceptable water Drinking Health: Severe acute health effects, even with short-term use. quality Drinking Aesthetic: Taste and appearance will lead to rejection of the water. Food preparation: Severe acute health effects, even with short-term use. Bathing: Serious effects on bathing or on bath fixtures. Laundry: Serious effects on laundry or on fixtures.  CLASSIFY THE WATER (c) WHEN IS WATER SAFE FOR USE? According to the classification system: Water in the Blue and Green classes is safe for lifetime use. Water in the Yellow class may be safe for use under certain conditions, but should be used with caution: - It is most important to sample and assess the quality of water in the Yellow class regularly. - Expert advice should be called upon to determine the real threat to sensitive users. - Sensitive groups should also be informed when water falls into the Yellow class. Water falling into the Red class should be considered unsafe for use and should be treated. Water in the Red class may be used for short-term emergency supply, but only where no alternative supplies are available. Water falling into the Purple class should be considered unsafe for use and should be treated. Water in the Purple class is unsafe even for short-term emergency use. 31  CLASSIFY THE WATER (d) WHAT ARE SENSITIVE GROUPS? Sensitive groups include people who may have particular medical conditions which make them more susceptible to poor water quality. Babies, young children and the elderly may also be more sensitive to some substances. v People differ widely in their responses to water quality. What is safe for one person is not necessarily safe for another. Even in the Blue (ideal) class, there may be a few individuals who show some negative response. Where a few individuals may experience negative effects, these individuals have been identified as "sensitive groups". v Babies are generally more susceptible to poor water quality, and are identified as "sensitive” for most substances. But it is important to note that not all babies will show negative effects, and that normal, healthy babies will not necessarily be affected. 32  CLASSIFY THE WATER (e) How is water classified ? The classification of water quality to determine its suitability for domestic use is a two step process. STEP 1 involves determining the class per substance for each of the domestic uses, namely drinking, food preparation, bathing and laundry. STEP 2 involves determining the overall class of the water supply. 33  CLASSIFY THE WATER (e) How is water classified ? STEP 1: Determine the class per substance for each of the domestic uses: i. Check to see if the data is shown in the same units as used in the Guidelines (see part 2). In most cases the concentrations in the tables are in milligrams per litre (mg/L]). ii. Compare the maximum and average concentrations of each substance to the concentration ranges in the left hand column of the Guidelines. The colour class of the substance is then read off in the columns for each use of domestic water in the right hand column. iii. For some substances (those which have acute effects only) only the maximum value is needed. For pH and for free available chlorine, both the maximum and minimum values should be used. An example of how to do this is shown in the case study. 34  CLASSIFY THE WATER (e) How is water classified ? STEP 2: Determine the overall class of the water supply: i. After comparing all the data to the guidelines, the worst class for a use (drinking, cooking or laundry and other uses) is used to determine the substance class as shown in Table on the next slide. The worst substance class will then determine the overall class of water supply. An example of how to do this is shown in Table D1 (p 26). 35  SUBSTANCE WORST CLASS PER USE SUBSTANCE CLASS Maximum value * Average value** 1. Blue not used*** Blue Faecal coliforms Green not used*** Green Total coliforms (cause acute effects – use maximum value only) Table 4: Classification of substances Yellow not used*** Yellow Red not used*** Red Purple not used*** Purple 2. Blue Blue Blue Electrical conductivity, turbidity, nitrate/nitrite, fluoride, sulphate, Green Blue/Green Green chloride, arsenic, zinc, cadmium, copper, iron, potassium, sodium, magnesium, calcium, hardness Yellow Blue Green Yellow Green/Yellow Yellow Red Blue/Green Yellow Red Yellow/Red Red Purple Blue/Green Purple Purple Red/Yellow/Purple Purple 3. As for 1, but use minimum value instead of maximum when pH values are below 7, Free available chlorine, or chlorine is below 0,3 mg/L pH 37  SECTION 4: DETERMINE TREATABILITY Can the water be Determine the What is the treated to remove What treatment is availability of purpose of problem required treatment: treatment? substances? What other How effective What treatment is methods can be should treatment available? used to improve be? water quality 38  DETERMINE TREATABILITY 1. WHAT IS THE PURPOSE OF TREATMENT? Water is treated to make it suitable for domestic use. Treatment requires sufficient removal of substances which cause water quality problems so as to make the water safe and acceptable. 2. DETERMINE TREATABILITY a) Identify the first substance of concern (Yellow, Red or Purple class). b) Identify possible treatment from Table on the next slide. c) Determine if treatment is economically and technically feasible with respect to the user. d) Identify next substance of concern and repeat steps (b) to (c) until all substances have been accounted for. 3. WHAT TREATMENT IS REQUIRED? The treatment required depends on: the substances in the water before treatment, the desired quality at the point of use, and the cost of treatment. 39  DETERMINE TREATABILITY Table 5: The classification of treatment options CHEAP Easy Treatment does not require trained people to administer. Chemicals or materials to treat the water are easy to obtain in the community or the home. Difficult Treatment requires trained people to supervise. Chemicals or materials to treat the water are usually readily available in the community or the home and are cheap. EXPENSIVE Easy Treatment does not require trained people to administer (easy to administer). Chemicals or materials to treat the water are expensive. Difficult Treatment requires trained people to supervise. Chemicals or materials to treat the water are expensive. 40  DETERMINE TREATABILITY Table 6: Some available treatment options for the improvement of microbiological quality TREATMENT VARIABLE Easy and expensive Difficult and cheap Difficult and expensive Easy and cheap Ultrafiltration Boil water Ozone Faecal coliforms & total Add household bleach Hypochlorites Fast sand filtration Chlorine dioxide coliforms Expose to sunlight Ultraviolet radiation Chlorine gas Slow sand filtration Chlorination Boil water Excess Free available chlorine Allow water to stand Activated carbon filtration - - in an open container 41  DETERMINE TREATABILITY Table 7: Some available treatment options for the improvement of physical quality TREATMENT VARIABLE Easy and cheap Easy and expensive Difficult and cheap Difficult and expensive TDS/Conductivity — Reverse osmosis — Ion exchange Electrolysis Chemical treatment, depending Low pH: Add lime and filter pH Columns with buffers on nature of problem, eg carbon — High pH: Add acid dioxide addition Sedimentation and filtration Conventional flocculation, Turbidity Disposable filtration kits — Slow sand filtration settling and filtration 42  DETERMINE TREATABILITY Table 8: Some available treatment options for the improvement of chemical quality TREATMENT VARIABLE Easy and cheap Easy and expensive Difficult and cheap Difficult and expensive Oxidation together with Flocculation with an iron salt (FeCI3), settlement and Arsenic - Ion exchange flocculation. settlement and filtration. Can be done as part of the normal treatment process. filtration Cadmium - Ion exchange — Chemical precipitation, settlement and filtration. Precipitation with sodium carbonate, settlement and filtration. This must be done as an additional step to the normal treatment Calcium Boiling of water Ion exchange — process. Ion exchange Reverse osmosis Chloride - Ion exchange — Electrolysis Chemical precipitation, settlement and filtration Copper - Ion exchange — Ion exchange Reverse osmosis Fluoride - Adsorption on activated — Re-activated alumina/bone char 43 alumina  DETERMINE TREATABILITY Table 8: Some available treatment options for the improvement of chemical quality (continued) (continued) TREATMENT VARIABLE Easy and Easy and cheap Difficult and cheap Difficult and expensive (continued) expensive Precipitation with sodium carbonate, settlement and Hardness, filtration. This must be done as an additional step to the — Ion exchange — Total normal treatment process, Ion exchange Oxidation through aeration. Operation is Removal as part of normal treatment Precipitation, sedimentation and filtration. Strong oxidants easy, but design requires process. High iron concentrations may Iron Ion exchange and/or high lime treatment. expertise. require additional chlorine for end- Add bleach and filter point chlorination. after allowing to settle. Precipitation with sodium carbonate, settlement and — filtration. This must be done as an additional step to the Magnesium Boiling of water Ion exchange normal treatment process. Ion exchange Nitrate/ Denitrification with anaerobic biological reduction. — — Nitrite Ion exchange Reverse osmosis Ion exchange Potassium — — Reverse osmosis Sodium Ion exchange Electrolysis 44 Sulphate  SECTION 5: INTERPRETATION OF WATER QUALITY INFORMATION What water quality Typical water problems are Interpret water quality problems in common in South quality information South Africa Africa? Can a water source When is water safe be developed for for domestic water supply? use? 45  TYPICAL WATER QUALITY PROBLEMS IN SOUTH AFRICA WHAT WATER QUALITY PROBLEMS ARE COMMON IN SOUTH AFRICA? The most important water quality problem in surface water in South Africa is most likely to be faecal pollution together with the associated disease-causing organisms. However, elevated salt concentrations (TDS, sodium and chloride) are also common in many parts of the country. In groundwater the most common problems are high nitrate/nitrite and fluoride concentrations. 46  TYPICAL WATER QUALITY PROBLEMS IN SOUTH AFRICA PROBLEMS IN SURFACE WATER Most of the surface water in South Africa is of good quality and requires only clarification and disinfection. There are, however, a few notable exceptions: 1. Faecal pollution High faecal and total coliform counts (used as indicator organism to indicate recent faecal pollution) occur in most surface water near dense human settlements. 2. Colour and stability The rivers that drain the mountain catchments along the southern coastline have waters that are highly coloured due to organic acids. These waters have characteristically low TDS (Electrical conductivity (EC)) concentrations and a low pH. Colour removal requires precise chemical dosing, and together with the stabilisation of the water, treatment is neither cheap nor easy. 47  TYPICAL WATER QUALITY PROBLEMS IN SOUTH AFRICA PROBLEMS IN SURFACE WATER 3. Salt concentrations (TDS or EC, sodium, chloride and sulphate) The rivers that drain the dry interior regions carry water that may have a high TDS concentration mostly resulting from high sulphate and chloride concentrations. This means that the water is corrosive and has a distinctly salty taste. Salt removal by means of reverse osmosis or ion exchange is expensive, and most communities accept the water after clarification and disinfection. The rivers that drain the northern and eastern parts of South Africa generally carry good quality water, unless it has been contaminated due to human activity. A prime example of this is the Vaal River downstream of the Vaal Dam, which has a high TDS due to effluent from the Witwatersrand area and from the gold mines. Treatment is expensive and the consumers normally accept the high salinity. 4. Eutrophication (high algal concentrations) Some reservoirs in South Africa have high algal concentrations. Water from these water bodies may have taste and odour problems. In many cases, authorities have implemented treatment options such as powdered activated carbon, or processes such as dissolved air flotation instead of the more conventional sedimentation in the clarification process. In some cases algae may produce toxins which are of concern to 48 human health. Generally, however, these toxins are also removed by the above processes.  SUBSTANCES OF CONCERN TO THE DOMESTIC WATER USER The groups have been selected according to the following criteria: GROUP A substances are general indicators of water quality and should be frequently tested at all the points in the water supply system. GROUP B substances are commonly present at concentrations which may lead to health problem and should always be determined before water is supplied. GROUP C substances occur less frequently at concentrations of real concern to health, but should always be tested in areas of the country where soft water of low pH value is used. GROUP D substances may commonly be present at concentrations of aesthetic and economic concern in domestic water sources. 49 MICROBIOLOGICAL WATER QUALITY GUIDELINES PHYSICAL WATER QUALITY GUIDELINES CHEMICAL WATER QUALITY GUIDELINES CHEMICAL WATER QUALITY GUIDELINES CHEMICAL WATER QUALITY GUIDELINES THANK YOU… 56