Public Health
Questions
- Why are there ‘health based’ and ‘aesthetic based’ values in the guidelines?
Values stipulated in the water guidelines include aesthetic based effects, the health based effects and the operational considerations. The health based values are important, as they are associated with contaminants, exposure levels, and the availability of the treatments and the analytical technologies. Aesthetic values on the other hand, include turbidity, tastes, and colour of water and help to indicate whether the consumer of the water will see it as drinkable. These values are important in the guidelines since they help in determining whether water has the correct palatability and portability effect to the consumer, that is, it is drinkable as well as portraying colour, taste and other characters that are appealing to the consumer’s senses.
- The health based guideline value for free chlorine is 5mg/L whereas the aesthetic based guideline value is 0.6mg/L – why are they different?
The health requirement for chlorine is 5mg/L above which the health regulation will indicate that chlorine is being detected in the water and it will compromise quality or the effectiveness of disinfection. At the same time, it will affect the reaction between chlorine and other organic precursors. However, the aesthetic value is based on consumer preference and sensitivity. At 0.6mg/L is the acceptable range for most consumers in terms of tastes and odour related to chlorine. Therefore, the difference exists because aesthetic value is based on consumer preference in terms of taste and odour while 5MG/l relates to the operational range of chlorine that will not be harmful.
- Why are different parameters monitored for source water and customer tap water? Give examples of parameters which require to be monitored in (a) raw water and (b) distribution system (ADWG Ch9/10 will help here)
Different parameters are monitored both at the source and at the customer’s water tap to ensure that surrogates are controlled and at the same time to increase assurance that objectionable characteristics are reduced or are not present. Some parameters that need to be monitored include PH, turbidity, dissolved oxygen, faecal contamination at the source water, treatment failures like free chlorine, HPC, Escherichia coli and turbidity, water stagnation issues like the dissolved oxygen, HPC, the loss of disinfectant residual and total coliforms, and in case there are disinfection by-products.
- Why is there ‘residual chlorine’ in drinking water? Why is the residual chlorine measured as ‘free’ residual chlorine in chlorinated systems, but as ‘total’ residual chlorine in chloraminated systems?
The presence of residual in the drinking water is an indication that a sufficient amount of chlorine has been put into the water so that most of the bacteria and viruses that are likely to cause diseases can be inactivated. At the same time, it helps in assuring the users that the water they are drinking or using for animal consumption has been protected from recontamination, as it is transported to their homes and when it will be stored at their homes. Chlorine presence also indicates the portability of water. In the chlorinated systems, the total demand for chlorine is zero since there are no nitrates to react with chlorine. Where the water is not treated, nitrate reacts with chlorine and part of it stays within the system to make the water portable.
- The results for tap water sourced from the Happy Valley system (DWQR p21) indicate that the aesthetic guideline for free chlorine was met 88.1% of the time – is this important?
The 88.1% of the time as indicated from the tap water of Happy Valley system is indicative of the aesthetic guideline and it is important because it shows that the palatable quality of water that is delivered to the residents of Happy Valley in terms of taste, colour and odour is not completely accepted by the residents. It indicates that 11.1% of the residents think that the waster is not good for consumption and therefore the water management board ought to do something about the matter to make it 100% good. It is also important because it explains the views of the thetic compliance has been fulfilled.
- Which parameters are used in measuring microbial contamination? (ADWG Ch10 will help here)
The parameters that are used to measure microbial contamination include the coliforms group. This group is made up of bacteria that have defined growth as well as biochemical characteristics that are related to faecal contaminants. It entails the total coliforms that can be used in disinfection of water, and it can also be used in treated water in the distribution system both ingress and regrowth as well as in outbreak investigations. Others of the coliform group include the Escherichia coli, and thermotolerant coliforms. Another parameter that can be used to measure microbial contamination includes the presence of enterococci and faecal streptococci. Enterococcus species originates from faecal matter. Faecal streptococci on the other hand are more resistant than the E. Coli and other coliform bacteria, they are resistant to drying and can therefore be used for routine controls and in the distribution systems. Ratio of counts is another parameter that counts thermotolerant coliforms and the faecal streptococci and helps in differentiating contaminations emanating from animals and humans. Others include the direct total bacteria counts and activity tests, heterotrophic bacteria, clostridium perfringens, heterotrophic plate count among others.
- The township of Parachilna achieves only 92% compliance for coliforms and yet 100% compliance for E.coli (DWQR p25). Explain the discrepancy in these results. Should the residents of Parachilna be concerned about these results?
The explanation for the discrepancies between coliform and E. Coli in Parachilna can be derived from the fact that unlike E. Coli, which is widely present in human and animal faeces, it is not found in other niches apart from faecal contamination. This therefore explains why it was 100% compliant. Coliform on the other hand found in faecal contamination, is also found naturally in the environment and therefore may not meet the 100% compliance. Since coliforms are not pathogens, they cannot be found in bottled water. This therefore means that they are not useful determinants of faecal contamination. The people of Parachilna should therefore not be concerned by the noncompliance of the coliforms.
- In the Barossa system (DWQR p20) the min value for coliforms recorded is 0 and the max value is 31. Given these results, explain why the average and median results are both also 0
Since this explains the water system in Barosa system, the whole system is not contaminated with coliforms. Thus, the median and minimum values read at zero. However, in case the water has contaminants, the maximum expected coliform in the water system is 31.
- What is THM, and why might it be important to measure it in drinking water?
THMs (trihalomethanes) are disinfection by-products that form once chlorine has been added to water that has high levels of organic particles like vegetations and decaying leaves. High HTMs are mostly found in areas with surface based water supply. It is important to test THMs in drinking water because if the levels exceed the required acceptable concentrations of 0.1mg/L, it can be dangerous to the health of the consumers. At the same time, drinking water that has a lot of THMs may in time lead to a person getting cancer.
- Why is it important to measure TDS?
TDS stands for total dissolved liquid and it is a meter that is used to analyse the quality of fresh water. TDS should be measured because when it reaches a certain level say 1000mg/l, the water is considered unfit to be consumed by human beings. TDS also measures taste of the water to determine if it is undesirable, that is, salty, metallic or even bitter. It is also used in measuring filter performance thereby determining when the filter should be changed. Also hardness of water can be detected as well as identifying whether the levels of minerals are constant for aquaculture. It helps measure hydroponics, pools and spas.
- What is the ‘rule of thumb’ figure used to convert electrical conductivity into total dissolved solids? Why does this conversion not always give a true picture of the TDS in a water sample?
The conversion factor is usually 0.67 which is multiplied by the approximate concentration usually given as (TDS) ppm = Conductivity µS/cm x 0.67. This conversion does not give the true picture of the TDS in the water sample because it is a gravitational analysis, which bases its assumption on the fact that a given sample would be measured to dryness and each party uses its own range to get the figures.
- Numerous country systems are never able to meet the aesthetic guideline values recommended for total hardness (DWQR p30). What issues might customers experience as a result of the utility’s inability to meet this guideline?
Generally, failure for the utility to meet the aesthetic guidelines indicates that many of the consumers will not be comfortable drinking the water, as they will think that it is impure. At the Same time, the consumers will think that it smells and tastes bad. It may also affect their clothing, as it may leave stains if it does not contain the water’s true colour.
- What does total hardness measure? Why does it have an aesthetic guideline but not a health based one?
Total hardness of water is the sum of calcium and magnesium ions concentrations that generally are expressed as the calcium carbonate equivalent. This being the case, total hardness measures the amount of calcium and magnesium that water may be having. Total hardness has an aesthetic guideline because it relates to the hardness that the consumer expects and is as a result of the source of the water. It is also based on aesthetic guidelines because it makes it difficult for consumers to obtain lather easily from it and can lead to undesirable deposits in hot water pipes and other fittings, and this can be expensive to remove. Health based requirements deal with the composition of water and the necessary steps that the water management takes to ensure that the water is safe for consumption by the consumer.
- Why might the values for both TDS and total hardness be relatively high in the source water of many country systems compared to the metropolitan systems?
The values for TDS and total hardness are high in the source water because at the source are plenty of inorganic salts and other organic matter that have not been filtered. At the metropolitan systems, filtration and sedimentation takes place and this minimises the level and amount of TDS and total hardness. At the source, residential runoffs, soil leaching pollution at point’s source are some of the reasons that explain water hardness and TDS. In the metropolitan system, chlorination makes the water soft and chemical contaminants are removed from this place.
- Why is it not possible to calculate the average pH value from a range of samples by simply adding the values and dividing by the number of samples taken? How would you go about calculating the average value from a list of pH results?
pH is a logarithmic scale and this being the case, it is impossible to take an average for a mixed solution since one has to determine the value of H+ in a solution, then total them and find the concentration of the ions in Mol/l of the new solution. The new pH can then be calculated.
- The result given for the minimum pH value of Murray Bridge source water is zero (DWQR p22). Why is this likely to be an incorrect result?
The pH value indicates the amount of hydrogen a given water point has. Owing to the fact that chemicals, contaminations, and pollutants are present everywhere, there ought to be a certain percentage of alkalinity in the water.
- Loxton, Morgan and Swan Reach appear to have significant issues in treating tap water to within the pH range required by ADWG (DWQR p28). Why might this be and what potential concerns maybe encountered by customers obtaining water with a pH consistently above 8.5?
The reasons as to why Loxoto, Morgan and Swan reach have issues in treating tap water may be because of the various networks of reservoirs and water mains that the water passes that affects the water pH. Water that has a high concentration of hydrogen ions is likely to pose concerns to the consumers in that the water will not be its natural texture like since high pH is likely to make the water slippery. At the same time, high pH levels are likely to change the taste of the water making it have the soda taste and at the same time the possibility of water having deposits are high.
- What does the term ‘true colour’ mean and what units are used to express this measurement?
True colour of water is the colour of water after water’s turbidity has been removed and it is as a result of the dissolved organics, the minerals and chemicals in water (American water association, 2003). The units used to express true colour are the colour units
- In tap water obtained from the Hope Valley system the average result for true colour is 20HU whereas the median result is 2 HU (DWQR p19). Why might these results be so different?
I think that the difference arises due to the number of samples taken. If a lot of samples have been taken with varying results; some being too high while the others too small, then the median could be low while the average becomes high. For example, in a sample of 20 samples with 1,2,4,2,8,3,5,45,56,86,3,8,5,12,,50,40,30,7 6,3. From the data, the median is 4.5 while the average is 17.
- In general what impact does increasing the number of samples taken have on the difference between the two measures of central tendency (average and median) reported in the tables?
From the example given above, if the number of samples increased at an increasing rate, then the median rate is bound to reduce while the average figure is likely to increase. This information depends on the value of the sample results such that if the values shift from high to low, the above results will be experienced, otherwise, if the values are closer to each other, then the measure of central tendency is likely to be closely related.
- Compare the results for a range of parameters (eg. colour, fluoride, TDS, turbidity) between source water and customer tap water from the same source. What can you say about the water treatment processes in regard to the comparison of the two results? Are the treatment systems across South Australia comparable in their removal of various parameters?
The source water usually has TDS, and turbidity, colour and fluoride. The components that the treatment process removes are TDS and turbidity as well as the colour. Fluoride is not removed in the process at each source. The same case happens in the treatment system across South Australia.
- Why do the values for some parameters actually increase during the treatment process? Which parameters fit into this category? Suggest reasons why this may be the case?
The values of some parameters increase during treatment because as the treatment takes place, chemicals are added to water. The effect of this is that these chemicals combine with the chemicals found in the water to form combinations. Some of the chemicals that fit into this category include oxygen.
What do you think are the main concerns that the public has about the quality of their water?
The main concern that the public has concerning the quality of water is that the water should have good taste and at the same time, the water is pure. This being the case, the public expects water that is both palatable and portable. The public expects to have water that is free from organics and other chemicals that can be harmful to their health and animals.
- Would the public prefer water which is palatable or potable? Explain the difference between these terms and cite examples which justify your response to the question.
Portable water can be consumed without there being any harmful effects. In other words, it is fit for consumption by animal and humans and is generally referred to as drinking water. Portable water may come from a natural source or it can be treated to ensure that it is safe for consumption. Usually, before water can be drunk in the developed countries, it is tested to find out if there are any harmful contaminants. Palatable water is that water that may be pleasing to drink but it does not necessarily mean that it is safe. However, it may be good tasting, have turbidity, lack sediments and have a pleasant colour that attracts the eyes. Overall drinking water should be both portable and palatable. Generally, the public would prefer water that is palatable given the fact that despite the fact that water is safe for drinking, if it does not have the required taste or have sediment, it will elicit comments from people saying that it is bad. For example, a region that has portable water that is impure may not consider that water to be pure. On the other hand, if a region has water that is palatable, everybody will like it irrespective of its state.
References
American Water Works Association. (2003). Water quality. Denver, CO: American Water Works Association.
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